This only occurred when you imported your backup? (to your brand new, freshly and successfully built error-free 3.1 stable server?)
OK, so I’d now start examining the data in your backup.
There was a recent topic about this and it may help.
What can i do ?
This was a subject of a fix last year, strangely.
@david forgive me for mentioning you, but this is completely relevant to that fix, would you care to chime in here?
I find solution
DO $$ BEGIN CREATE TYPE hotlinked_media_status AS ENUM('downloaded', 'too_large', 'download_failed', 'upload_create_failed'); EXCEPTION WHEN duplicate_object THEN null; END $$;
20220428094026_create_post_hotlinked_media.rb
You edited the Rails migration within the container and that allowed you to complete the import?
yes, that’s right
That’s great, well done! 
thanks for your help 