[ksooo]

Does this happen after you 'clear data' in settings-pvr livetv-general ?

Manually created groups in kodi will be gone after doing this. If the backend provides the groups they will be reloaded from it in kodi.

Just tried with a backend with, and one without providing channels groups. My manual groups are gone.

I don't remember doing a "clear data" the last time it happened.  However, the CoreELEC box had locked up and I had to do a manual power cycle.

Deactivate sync groups with backend in Kodi PVR settings. Look at the help text for explanation why this solves your problem.