Okay well, didn't test for a couple of days and not appointments for this user are showing. "Events on Office calendar affects availability" was enabled. However, what's not working is that customers can still book a time slot although it shouldn't show up on the booking page.
Staff A and B are both blocked at 2pm. but the customer still sees the slot as bookable. Only if User A is removed from staff the slot disappears from the booking page. User A is the user that was affected from the initial problem I opened this thread for. So staff A's availability basically has no bearing on booking page availability. Could it be because this user is the admin?