It happens to me all the time ( raspberry 3) on previous versions and rc4 .
I tried rebooting it few times nothing helps
How many time did u restarted it ?
The only way I find it easy to fix the issue when it suddenly happens it’s soft reset the LibreELEC and works again
So I’m tired adding on the sources so I made the back up and restoring it its seems to be working and my Addons and builds are there
I don’t know what causes it a bug ?