Despite the newest update which was supposed to cure the issue, the infinite catering services loop is still very much alive and kicking in the Majestic Q400.
The latest update wasn't supposed to fix the catering service never ending, it was the boarding that never ended. I wasn't aware of a never ending catering instead.
Once called for, the service does not end, the menu keeps showing Catering Vehicles Are On Their Way and other services obviously cannot commence their relevant tasks.
That doesn't seem the service doesn't end, if the menu shows Catering Vehicles Are On Their Way, it means the catering vehicles haven't arrived yet, so the service is not even starting.
Or, are you really seeing a Catering Vehicles Are On Their Way, while or after the service has started (catering services servicing) and it doesn't go away ?
In any case, as with every other report, I just tried it now, and the catering arrives, starts and ends normally.
Are you using a custom configuration for the airplane ? If yes, try to Reset it to the one that comes with GSX.
Does it happen on a specific airport ? Please provide reproduction steps, like the gate used, and airport used (possibly an FSDT or a default one), and the exact sequence of operations you choose in GSX.