My C8 hub got corrupted, apparently, by running for weeks with a low memory warning, and then when it finally crashed, it would reboot to a spinning UI page, lockup, and start a cycle of auto-rebooting. No usual stuff would get it working (rebuilding database, power cycling), so I did a soft reset and restored the last backup. The issue was still there. I then found over the next few hours that all my backups taken while the memory was low were also corrupted in the same way, making the hub unusable. I tried each backup in progression backwards, both with upgrading the backup to the current platform version, and trying the version of the platform of the backup (so time consuming). It appeared that all the backups that I had, taken over the weeks I ran with the memory low warning, exhibited the same UI behavior, making the hub unusable.
Everything in the UI was quick and stable when booting to safe mode, so I knew it was not the hub itself. Even disabling all apps and drivers in safe mode wouldn't fix the issue on next full reboot. At 2pm Friday I pulled the trigger and ordered a C8 Pro, even though I didn't have a functioning hub back yet to migrate to it, but clearly I had pushed the limits of the C8 for too long... I continued recovering backups, changing platform versions.... none of them were working and the dates were all within the timeframe I let the hub run with low memory. 
Then I suddenly realized as I got close to the last couple backups to try restoring, that the last two of my local backups on the hub were actually from February, three months ago, instead of the recent weeks like all the other backups that were corrupted. I had to redo a bunch of stuff I did on the hub since then, but a Feb 14th backup that was still hanging around saved me from losing years of work. I'm not sure how long it would have taken me to start over again.
So, whoever at Hubitat decided that the hub should keep around a couple local backups from months ago, thank you! If it were not for that Feb 14th backup that finally fixed the hub UI issues, I would have been in a sorry state. This was the closest I have ever come to losing everything, and I have a lot of stuff on my C8 that would have been daunting to recreate.
Now, onward to the C8 Pro! 
It arrived in 24 hours, I didn't even notice it was delivered yesterday. The C8 is very stable right now, and I have now redone everything I lost since February (I added too much in those three months so it was painful), so I'm going to take a week breather before upgrading to the Pro.