OS X Catalina seems to shut down during sleep
This is usually a problem with the 'deep sleep' / hibernation mode macOS uses. Basically, when you close the lid your Mac goes in standby mode. After some time has passed, your Mac goes into hibernation mode to save more battery. As it seems, your Mac isn't properly able to either go into hibernation mode, or recover from hibernation mode, causing your OS to simply reboot.

Resetting SMC sometimes fixes the issue, but there's a lot unclear about these errors. Some users have stated that resetting SMC works, but only if FileVault is disabled.