I have been using Trakt for years now and slowly but surely I have been adding and adding to my collection and watchlists, and dealing with all the issues with some services like CinemaHD pulling from one list and other services pulling from another… resigning myself to not complaining and making it work, but to my surprise though, recently I had time to again start watching some of the movies, and my collection went from several thousand to 490… where did everything else go? I thought maybe it was a glitch on one device, but when I look all of them now show 490 in the collection, a bit more under watchlist, because I mostly use that for series I am tracking, but all the movies I had curated in my collections are GONE, and I can’t fathom how long it will take to compile that list again, and how many obscure names that I’d added to eventually watch, or re-watch as one gets older and perspectives change… Where did they all go? 
I’m sorry but that’s the danger of letting other applications remove stuff from Trakt. Especially if you use multiple.
Also if it’s about the watchlist. Items get removed when you watch them after you added them.
So say you have watched all of Friends and add it to the watchlist it’s fine and it will stay on it.but as soon as you track any episode it’ll be removed. Same for movies.
With collections. Some media centers are set up that they can add and remove stuff. Pretty sure you can also set it like it can only push new data.
So in the case of CinemaHD in the trakt sync mode, it should be left to “use trakt data only” and not “merge local and trakt data”?
I’m not sure on that. But I read in another thread that cinemahd uses the trakt collection feature as their favorites list. Maybe that’s also an issue you’re facing.