[Varstahl]

Would the update(I don't recall losing watch status in the past, I also updated Kodi to 18.5) have something to do with the cache getting cleared?

There are two types of cache, what I called the "catalog" cache (listings of sections like you would see in a browser, list of movies and tv series) and "video data" cache (thumbnails, duration, posters, video stream URLs, number of episodes, synopses, etc). The general catalog cache, like the Watchlist, gets reset every ~11 hours, while the video data is more aggressively and permanently cached. For example, if a season is listed with 4 episodes and you go in the next week when the 5th is out, you will still see 4 episodes unless you refresh the season/tv show, because updating the cache is very expensive in terms of resources and bandwidth and very rarely useful. On the other hand, you would have seen that the brand new TV show that's been added the day before is correctly shown in the list of TV series, because the presence of the show in a certain category is only stored in the catalog cache.

I hope that this clears some of the confusion.

Just a quick thanks for all you hard work on this add-on @Varstahl, family really happy that  0.7.8 is all up and working again!

Glad the family's happy

Since 0.7.7 I can't get HD or Full HD resolution anymore

I'm sorry to be the one to break the news for you, but you didn't get FHD, let alone HD, for almost a year now. HD is tied to HDCP, which Kodi can't provide, can't remember if FHD as well or if FHD straight up requires Google's hardware. Amazon went the opposite side of Netflix and bolted everything shut. Post and long a** thread for reference.