diff --git a/service/controllers/SyncController.php b/service/controllers/SyncController.php
index eff0c06f..988acbfa 100644
--- a/service/controllers/SyncController.php
+++ b/service/controllers/SyncController.php
@@ -11,6 +11,12 @@ public function indexAction()
         $db = Globals::getDBConn();
         $json = Zend_Filter::filterStatic($this->getRequest()->getParam('json'), 'StripTags');
 
+        // Sanitize incoming JSON to remove invalid activity values (e.g., empty strings)
+        $sanitized = $this->sanitizeSyncJson($json);
+        if ($sanitized !== null) {
+            $json = $sanitized;
+        }
+
         $sync = new SyncModel();
 
         if ($sync->commit($json))
@@ -24,4 +30,97 @@ public function indexAction()
         }
     }
 
+    /**
+     * Sanitizes the provided sync JSON by removing invalid/non-numeric entries from
+     * each count's activities array and converting numeric strings to integers.
+     * Returns a sanitized JSON string if any changes were made, otherwise returns null
+     * to indicate no changes.
+     *
+     * @param string $json The sync JSON to sanitize
+     * @return string|null The sanitized JSON string, or null if no changes were made
+     */
+    private function sanitizeSyncJson($json)
+    {
+        // Ensure $json is a string and not empty
+        if (!is_string($json) || $json === '') {
+            return null;
+        }
+
+        // Attempt to decode the JSON string
+        $decoded = json_decode($json, true);
+        if ($decoded === null || $decoded === false) {
+            // If the JSON string is malformed, let SyncModel handle logging
+            return null;
+        }
+
+        // Check that the decoded JSON has a 'sessions' key containing an array of sessions
+        if (!isset($decoded['sessions']) || !is_array($decoded['sessions'])) {
+            return null;
+        }
+
+        // Initialize a counter to keep track of how many count's activities arrays were modified
+        $changedCounts = 0;
+
+        // Iterate over each session in the decoded JSON
+        foreach ($decoded['sessions'] as &$session) {
+            // Check that the session has a 'counts' key containing an array of counts
+            if (!isset($session['counts']) || !is_array($session['counts'])) {
+                // If the session is missing a 'counts' key, skip it
+                continue;
+            }
+
+            // Iterate over each count in the session's counts array
+            foreach ($session['counts'] as &$count) {
+                // Check that the count has an 'activities' key containing an array of activities
+                if (!isset($count['activities']) || !is_array($count['activities'])) {
+                    // Ensure activities is an array
+                    $count['activities'] = array();
+                    continue;
+                }
+
+                // Initialize a variable to keep track of the original activities array
+                $original = $count['activities'];
+
+                // Initialize an empty array to store the filtered activities array
+                $filtered = array();
+
+                // Iterate over each activity in the count's activities array
+                foreach ($original as $a) {
+                    // If the activity is an integer, keep it
+                    if (is_int($a)) {
+                        $filtered[] = $a;
+                    } elseif (is_string($a)) {
+                        // Keep numeric strings, cast to int; drop others (including empty strings)
+                        if ($a !== '' && ctype_digit($a)) {
+                            $filtered[] = (int)$a;
+                        }
+                    }
+                    // drop all other types (null, arrays, objects, floats, etc.)
+                }
+
+                // Check if the filtered activities array is different from the original
+                if ($filtered !== $original) {
+                    // If the filtered activities array is different, update the count's activities array
+                    $count['activities'] = $filtered;
+                    // Increment the counter to keep track of how many count's activities arrays were modified
+                    $changedCounts++;
+                    // Log the changed session info
+                    Globals::getLog()->info('SYNC SANITIZE - changed session: '.$session['id'].' - count: '.$count['id']);
+                }
+            }
+            unset($count);
+        }
+        unset($session);
+
+        // Check if any count's activities arrays were modified
+        if ($changedCounts > 0) {
+            // If any count's activities arrays were modified, log the number of modified counts
+            Globals::getLog()->info('SYNC SANITIZE - cleaned counts: '.$changedCounts);
+            // Return the sanitized JSON string
+            return json_encode($decoded);
+        }
+
+        // If no count's activities arrays were modified, return null
+        return null;
+    }
 }