I’ve looked at the description of the cat enforced races and compared it to the 3R races.
How do you tell from the description if a race is mass start (see all cats) vs single cat?
On Zwiftpower there’s an incognito icon (amongst others) which means the categories can’t see one another:
Often when the categories start a minute after each other (in order A, B, C, D) they’re set for the categories to not be able to see each other.