Hello, It has been many years since I last played. I tried to play today, but all my characters "required" a rename. I can see that policies change and such but there is no way that all names would ...
Sorry to hear you had to rename your characters, as @Fenril2014 pointed out this may not be to do with inappropriate names but may instead be due to the server merge that happened back in 2017.
If you run into any other issues be sure to let us know.