@Peter has looked at this for you and somehow you have display groups not owned by a user.
There was an old bug along those lines, so it’s potentially something historical that has slipped under the radar so to speak.
We’re fairly certain you’d have seen the same in 2.3 though, and can’t explain why you didn’t right now.
You can run the following SQL on your 3.0.0 database to resolve that issue:
UPDATE `displaygroup` SET userId = (SELECT userId FROM `user` WHERE usertypeid = 1 LIMIT 1) WHERE userId NOT IN (SELECT userId FROM `user`);
If you need guidance on running SQL commands, there’s a document here which explains for a Docker-based installation: