As of right now you can mark a item as collected with one type of metadata bluray/dvd/digtal ect.
Myself I have multiple editions of a movie like a bluray and a dvd or bluray and digital copy or all of the above.
It would be nice to either be able to mark a movie/tv show/episode as collected more than once.
Like watch history with a view all button and the best quality shown on the main page.
Or be able to select more than one option under format.
I personally prefer the former because it represents what is an entirely different copy.

Hope this makes sense.

It is a bug, and here are steps to reproduce:
1. Open an episode link on the website (or movie)
2. Check-in the episode
3. Watch it (can be escaped)
4. Rate the episode
You will find the watch count is 2, it should be 1.

What did I do to go around it?
After I check-in an episode, I manually refresh the webpage, then after I rate the episode.
So a manual refresh is mandatory after checking-in in order to not duplicate your watching history.

I guess a possible solution might be a force update to the cache and to the webpage after the check-in to simulate a manual refresh.
Or, after check-in, force the webpage to refresh.

Reelgood, Trakt's (primary?) "Watch Now" data partner, could possibly provide this information somehow with an update to the existing two-way sync feature, if implementing Trakt's own UI for it isn't feasible due to available dev time etc.

The main use cases I see are filtering lists and other views to show only content the user has access to through a service subscription, and prioritizing which two "Watch Now" buttons get the prime slot below the poster image on pages where that applies. (Right now, even shows that are available on e.g. Hulu display Amazon & iTunes purchase options there, forcing the user to open the "Watch Now" modal to access the streaming option they already pay for.)

See https://support.trakt.tv/forums/188762-general/suggestions/17409505-filter-based-on-watch-now-services-that-i-subscr for a related idea (the first use case).

The same way there's now a fast switch for dark mode in the main menu (Dark Knight Mode), I think it would be interesting the have a quick method to turn spoilers on and off. For example, when browsing lists, specially when there are lots of special episodes, sometimes I need to click on several items to reveal their titles, because "Special 34" doesn't give as much information as "6x03", and it becomes tiresome pretty fast. Going to settings to temporarily turn spoilers off and later turn them on isn't ideal either. I think a switch where a single click is needed would be fantastic.

I keep a tab open on Trakt in Firefox for Android at all times and come back to it whenever I need to file something as watched. Because of the caching system in Firefox (possibly just for Android?), sometimes the tab is being loaded from the local cache instead of from the server.

When it does this, I'm no longer connected to the server, and trying to mark shows gives me an error saying "You are already signed in." To get the site back into working condition, I need to hit reload in Firefox to force it to establish a connection or whatever is going on in the background.

I'm no web developer, but my suggestion would be some kind of Javascript that polls for a connection to the server and triggers a page reload if the connection is not being made, or even just throws a warning. "Connection lost, click here to reload" if you don't want to trigger a reload without user input.

Would it be possible to add some way to flag duplicates directly on the site?

For example adding a link "this is/has a duplicate" next to the "refresh data" that open a pop-up where you can enter a link to the duplicate/original of a movie/show, maybe even a comment if details are needed.
It would be easier and quicker for user to inform you about them and you could even see the links that are flagged more often and correct them first.

It would reduce the number of support messages and make duplicate/error signaling accessible to the less curious of us who never checked what the "Help" link was about or never had the motivation to search and find out how to signal a duplicate.