Just saw this on my Paper 1.16.5 server as I was restarting. Not sure how critical it is.

24.09 20:47:33 [Server] ERROR Nag author: 'MaxTheGinus' of 'DriveBackupV2' about the following: This plugin is not properly shutting down its async tasks when it is being shut down. This task may throw errors during the final shutdown logs and might not complete before process dies.

Does this always happen on server shutdown?

I just did a shutdown again to test and it didn't throw the same error.

Sounds to me like the plugin was mid sending a http request (probably an update check) whilst the server was shutting down. The chances of this happening is pretty rare so while I could spend time to look into and fix it, I’ll leave unless some major issue is linked to it.