Maybe check if your phone is stopping apps that are in the background. If I’m not mistaken it’s an Android feature and most of the time you can disable it in settings per app. On my Huawei phone it’s Settings > Apps > the app > power usage > launch settings.
Is it just me or does KDE Connect only work about half the time?
If I have my phone unlocked and the app open it seems to work on my computer but after a while it just seems to stop working completely.