Hello @Joachim_Herbert,
As @Geoff_Coupe @Richard_Tywoniak @Mike_O_Neill and others here have suggested this type of behavior typically indicates a streaming service hack. I’m sorry you had to experience this.
If you haven’t done so already I suggest setting a new password on your Tidal account and then resyncing your Tidal account with Roon.
Additionally, I’d go to Setting>Backups>Back now>Backup after resyncing and checking your library to ensure that there aren’t any outliers in there. That way you’ll have a clean backup without any unwanted Tidal content from your account breach.