osx catalina randomly ejecting drives

Are you using this for Time Machine backups? You could first launch Disk Utility app and run First Aid to see if there are any obvious problems.

If you have any sensitive data on there you want to preserve, I would copy it to another drive. After that you could do a reformat and remount to see if that solves the issue and make it stable again.

Disk Utility can be found in your Utilites folder. The problem could also be with a failing UBS between the drive and the computer.