The input lock "KACControlLock" trigger area doesn't scale with the KSP UI Scale setting. So if you play with a non 100% scale, the input lock area is in a location other than the actual KAC window.
See in the screenshot, the cursor is just over empty space, but the input lock is active. This is with 150% UI scale. If I set the UI scale back to 100%, everything works as expected.
The input lock "KACControlLock" trigger area doesn't scale with the KSP UI Scale setting. So if you play with a non 100% scale, the input lock area is in a location other than the actual KAC window.
See in the screenshot, the cursor is just over empty space, but the input lock is active. This is with 150% UI scale. If I set the UI scale back to 100%, everything works as expected.