When I add a future TV show to my watchlist, I see them premiere on my calendar. For example on the 10th of august I see 'I am Groot" premiere on my calendar.
The calendar view is actually run through our search service, so I’m wondering if you’re hitting a filter limit. Behind the scenes, we build that calendar by sending a huge list of IDs that would include all movies you’ve watched, collected, or have your watchlist (we then remove anything you’ve hidden).
My guess is that number of IDs is large and might be truncating some items. That could explain why it works for some people (Prey shows up for me for example) but not others.