I have bluetooth connections enabled in kdeconnect and the android app, and everything works notification-wise. However, when my computer comes out of sleep mode, kdeconnect lists my device as unreachable. I have to manually open the kdeconnect devices menu and click "refresh" while my phone is unlocked for it to recognize the device again.
This is true for me as well, but connected over wifi instead of Bluetooth.
Reconnection on Android 9+ should be much better since https://invent.kde.org/network/kdeconnect-android/-/commit/fd34e56675dd7e982e22abb051400804ab5ede67 Please reopen if it isn't.