diff --git a/.gitignore b/.gitignore
index e7b13c9f..3180a079 100644
--- a/.gitignore
+++ b/.gitignore
@@ -56,6 +56,7 @@ dkms.conf
 
 segger/Output
 _build/
+cmake-build-*/
 bin/
 *.emSession
 *.jlink
@@ -68,4 +69,3 @@ Makefile.user
 
 # Exclude all SoftDevice S340 files
 lib/softdevice/s340*
-
diff --git a/lib/sdk11/components/libraries/bootloader_dfu/bootloader.c b/lib/sdk11/components/libraries/bootloader_dfu/bootloader.c
index bd9b8cce..059b6fdd 100644
--- a/lib/sdk11/components/libraries/bootloader_dfu/bootloader.c
+++ b/lib/sdk11/components/libraries/bootloader_dfu/bootloader.c
@@ -48,12 +48,29 @@ typedef enum
     BOOTLOADER_RESET_TO_SELF,                           /**< Bootloader status field for indicating that a reset has been requested and current update process should be aborted and the bootloader must be reentered. */
 } bootloader_status_t;
 
-static pstorage_handle_t        m_bootsettings_handle;  /**< Pstorage handle to use for registration and identifying the bootloader module on subsequent calls to the pstorage module for load and store of bootloader setting in flash. */
-static bootloader_status_t      m_update_status;        /**< Current update status for the bootloader module to ensure correct behaviour when updating settings and when update completes. */
-static bool m_cancel_timeout_on_usb; /**< If set the timeout is cancelled when USB is enumerated. Otherwise, the timeout is only cancelled when DFU update is started. */
-
-APP_TIMER_DEF( _dfu_startup_timer );
-volatile bool dfu_startup_packet_received = false;
+static pstorage_handle_t        m_bootsettings_handle;  /**< Pstorage handle to use for registration and identifying the bootloader module on subsequent calls to the pstorage module for load and store of bootloader setting in flash. */
+static bootloader_status_t      m_update_status;        /**< Current update status for the bootloader module to ensure correct behaviour when updating settings and when update completes. */
+static bool m_cancel_timeout_on_usb; /**< If set the timeout is cancelled when USB is enumerated. Otherwise, the timeout is only cancelled when DFU update is started. */
+static bool m_usb_was_mounted; /**< Tracks whether the USB DFU session was ever enumerated so we can exit when cable is later removed. */
+static bool m_startup_dfu_has_activity; /**< Tracks whether any valid serial or UF2 update traffic has started. */
+
+APP_TIMER_DEF( _dfu_startup_timer );
+
+static void bootloader_timeout_startup_dfu(void)
+{
+    if (!m_startup_dfu_has_activity)
+    {
+        dfu_update_status_t update_status;
+        update_status.status_code = DFU_TIMEOUT;
+
+        bootloader_dfu_update_process(update_status);
+    }
+}
+
+void bootloader_dfu_activity_mark(void)
+{
+    m_startup_dfu_has_activity = true;
+}
 
 /**@brief   Function for handling callbacks from pstorage module.
  *
@@ -79,26 +96,20 @@ static void pstorage_callback_handler(pstorage_handle_t * p_handle,
 /* Terminate the forced DFU mode on startup if no packets is received
  * by put an terminal handler to scheduler
  */
-static void dfu_startup_timer_handler(void * p_context)
-{
-#ifdef NRF_USBD
-  if (m_cancel_timeout_on_usb && tud_mounted())
-  {
-    return;
-  }
-#endif
-
-  // nRF52832 forced DFU on startup
-  // No packets are received within timeout, exit DFU mode
-  // dfu_startup_packet_received is set by process_dfu_packet() in dfu_transport_serial.c
-  if (!dfu_startup_packet_received)
-  {
-    dfu_update_status_t update_status;
-    update_status.status_code = DFU_TIMEOUT;
-
-    bootloader_dfu_update_process(update_status);
-  }
-}
+static void dfu_startup_timer_handler(void * p_context)
+{
+#ifdef NRF_USBD
+  if (m_cancel_timeout_on_usb && tud_mounted())
+  {
+    m_usb_was_mounted = true;
+    return;
+  }
+#endif
+
+  // nRF52832 forced DFU on startup
+  // No update activity is received within timeout, exit DFU mode
+  bootloader_timeout_startup_dfu();
+}
 
 /**@brief   Function for waiting for events.
  *
@@ -126,14 +137,29 @@ static void wait_for_events(void)
     // Event received. Process it from the scheduler.
     app_sched_execute();
 
-#ifdef NRF_USBD
-    // skip if usb is not inited ( e.g OTA / finializing sd/bootloader )
-    if ( tusb_inited() )
-    {
-      tud_task();
-      tud_cdc_write_flush();
-    }
-#endif
+#ifdef NRF_USBD
+    // skip if usb is not inited ( e.g OTA / finializing sd/bootloader )
+    if ( tusb_inited() )
+    {
+      tud_task();
+      tud_cdc_write_flush();
+    }
+
+    if (m_cancel_timeout_on_usb)
+    {
+      if (tusb_inited() && tud_mounted())
+      {
+        m_usb_was_mounted = true;
+      }
+      else if (m_usb_was_mounted &&
+               !(NRF_POWER->USBREGSTATUS & POWER_USBREGSTATUS_VBUSDETECT_Msk))
+      {
+        // Only exit startup DFU after USB was actually unplugged, not on a host-side
+        // re-enumeration or temporary unmount.
+        bootloader_timeout_startup_dfu();
+      }
+    }
+#endif
 
     if ((m_update_status == BOOTLOADER_COMPLETE) ||
         (m_update_status == BOOTLOADER_TIMEOUT) ||
@@ -353,15 +379,17 @@ uint32_t bootloader_init(void)
 }
 
 
-uint32_t bootloader_dfu_start(bool ota, uint32_t timeout_ms, bool cancel_timeout_on_usb)
-{
-  uint32_t err_code;
-
-  m_cancel_timeout_on_usb = cancel_timeout_on_usb && !ota;
-
-  // Clear swap if banked update is used.
-  err_code = dfu_init();
-  VERIFY_SUCCESS(err_code);
+uint32_t bootloader_dfu_start(bool ota, uint32_t timeout_ms, bool cancel_timeout_on_usb)
+{
+  uint32_t err_code;
+
+  m_cancel_timeout_on_usb = cancel_timeout_on_usb && !ota;
+  m_usb_was_mounted = false;
+  m_startup_dfu_has_activity = false;
+
+  // Clear swap if banked update is used.
+  err_code = dfu_init();
+  VERIFY_SUCCESS(err_code);
 
   if ( ota )
   {
@@ -369,15 +397,13 @@ uint32_t bootloader_dfu_start(bool ota, uint32_t timeout_ms, bool cancel_timeout
   }else
   {
     // DFU mode with timeout can be
-    // - Forced startup DFU for nRF52832 or
-    // - Makecode single tap reset but no enumerated (battery power)
-    if ( timeout_ms )
-    {
-      dfu_startup_packet_received = false;
-
-      app_timer_create(&_dfu_startup_timer, APP_TIMER_MODE_SINGLE_SHOT, dfu_startup_timer_handler);
-      app_timer_start(_dfu_startup_timer, APP_TIMER_TICKS(timeout_ms), NULL);
-    }
+    // - Forced startup DFU for nRF52832 or
+    // - Makecode single tap reset but no enumerated (battery power)
+    if ( timeout_ms )
+    {
+      app_timer_create(&_dfu_startup_timer, APP_TIMER_MODE_SINGLE_SHOT, dfu_startup_timer_handler);
+      app_timer_start(_dfu_startup_timer, APP_TIMER_TICKS(timeout_ms), NULL);
+    }
 
     err_code = dfu_transport_serial_update_start();
   }
diff --git a/lib/sdk11/components/libraries/bootloader_dfu/bootloader.h b/lib/sdk11/components/libraries/bootloader_dfu/bootloader.h
index 9b6f7540..5c68e9bc 100644
--- a/lib/sdk11/components/libraries/bootloader_dfu/bootloader.h
+++ b/lib/sdk11/components/libraries/bootloader_dfu/bootloader.h
@@ -68,11 +68,18 @@ void bootloader_app_start(void);
  */
 void bootloader_settings_get(bootloader_settings_t * const p_settings);
 
-/**@brief Function for processing DFU status update.
- *
- * @param[in]  update_status DFU update status.
- */
-void bootloader_dfu_update_process(dfu_update_status_t update_status);
+/**@brief Function for processing DFU status update.
+ *
+ * @param[in]  update_status DFU update status.
+ */
+void bootloader_dfu_update_process(dfu_update_status_t update_status);
+
+/**@brief Mark that startup DFU has received valid update activity.
+ *
+ * @details This suppresses the startup timeout or USB unplug fallback that is only
+ *          meant for the "entered bootloader, but never started an update" case.
+ */
+void bootloader_dfu_activity_mark(void);
 
 /**@brief Function getting state of SoftDevice update in progress.
  *        After a successfull SoftDevice transfer the system restarts in orderto disable SoftDevice
diff --git a/lib/sdk11/components/libraries/bootloader_dfu/dfu_transport_serial.c b/lib/sdk11/components/libraries/bootloader_dfu/dfu_transport_serial.c
index 71f08526..b8c65ae3 100644
--- a/lib/sdk11/components/libraries/bootloader_dfu/dfu_transport_serial.c
+++ b/lib/sdk11/components/libraries/bootloader_dfu/dfu_transport_serial.c
@@ -10,10 +10,11 @@
  *
  */
 
-#include "dfu_transport.h"
-#include <stddef.h>
-#include "dfu.h"
-#include <dfu_types.h>
+#include "dfu_transport.h"
+#include <stddef.h>
+#include "bootloader.h"
+#include "dfu.h"
+#include <dfu_types.h>
 #include "app_error.h"
 #include "app_util.h"
 #include "hci_transport.h"
@@ -197,9 +198,8 @@ static void process_dfu_packet(void * p_event_data, uint16_t event_size)
     uint32_t              index;
     dfu_update_packet_t * packet;
 
-    // Adafruit modification for startup dfu
-    extern bool dfu_startup_packet_received;
-    dfu_startup_packet_received = true;
+    // Mark that startup DFU has transitioned into a real update flow.
+    bootloader_dfu_activity_mark();
 
     while (false == DATA_QUEUE_EMPTY())
     {
diff --git a/src/usb/msc_uf2.c b/src/usb/msc_uf2.c
index 96d705bc..f4a60787 100644
--- a/src/usb/msc_uf2.c
+++ b/src/usb/msc_uf2.c
@@ -145,9 +145,19 @@ int32_t tud_msc_write10_cb (uint8_t lun, uint32_t lba, uint32_t offset, uint8_t*
   uint32_t count = 0;
   while ( count < bufsize )
   {
+    int written;
+
     // Consider non-uf2 block write as successful
     // only break if write_block is busy with flashing (return 0)
-    if ( 0 == write_block(lba, buffer, &_wr_state) ) break;
+    written = write_block(lba, buffer, &_wr_state);
+    if ( written > 0 )
+    {
+      bootloader_dfu_activity_mark();
+    }
+    else if ( written == 0 )
+    {
+      break;
+    }
 
     lba++;
     buffer += 512;