We have found sometimes people accidentally put a white space at the start or end of their appointment type categories. This can cause two separate categories to show up in online bookings (when it should be one).
Now when you save a category for your appointment types, we look to see if there is a leading or trailing white space, and if so, we remove it.
Every little thing helps!
UPDATE: We also applied this to Expense Vendor and Expense Category as per the request in the comments.