Android forgetting default launcher every few minutes

Starting last week, my HTC One running ARHD 31.5 keeps forgetting the default launcher. Every few minutes, it will forget the setting and ask me for a launcher when I hit the home button. So far, I haven't found a pattern yet. Here's what I've tried so far: - restarting the phone - removing the default setting via Settings > Apps and setting it fresh - tried different launchers to rule out the launcher deleting the settings - updating the ROM (seriously) It happens both when the phone is locked, or when I keep it unlocked and basically not doing anything but keeping the screen alive. After a few minutes, the default will be gone. Any ideas how to debug this are welcome.