This look like the same issue than Tools_migrations_migrate failed because of a remaing earsed domain - #3 by Beurt
You can probably fix the issue by running
nano /etc/yunohost/apps/nextcloud/settings.yml
remove the line about skipped_regex:
and save/exit with Ctrl+X and Y to confirm
then in the webadmin, re-run the migration by going in Tools > Migrations