Series based on this TVDB entry was removed. Why?
https://thetvdb.com/series/the-cartoon-cipher
https://thetvdb.com/series/zeria
Because they are just another vlogger and amateur content.
If it’s not an actual web series and also not on tmdb enough reason to nuke it.
Already a miracle how it’s on thetvdb but if no one reports it 
The content is certainly professional and not at all amateur.
It has been on Trakt for years not and just because it’s not on TMDB is not a good reason to nuke it because TMDB has different policies.
Not at all a miracle because TVDB allows it. Like many others that are on Trakt.
No reason to delete them. Just leave them be.
So, which professional worked on those YouTube videos? Or which professional studio produced this content?
People who blog about anime (in this case) are not professionals. No matter how popular a blog may or may not be. Professionals are people who worked or started on/in other stuff in the tv/movie industry before.
Tvdb has apparently no (longer?) any guidelines about the amateur content. So looks like anything posted on YouTube is fair game now lmaaaoo. Waiting for someone to start adding asmr videos to the database. 
The people who made these videos.
So the threshold for being a professional and being allowed on Trakt is working for Netflix or HBO?
Why should independent content not be allowed? Just because it’s uploaded on YouTube?
Well this is an absurdly restrictive definition of professional.
No, professionals are people who who do something for a living.
And if TVDB was still connected, it should be allowed on Trakt. Literally why not. It affects you in no way and it would be nice to track exactly when I watched such videos.
Amateur content per TMDb (and for what it’s worth also on MyAnimeList and anidb. Though this is not anime.) which Trakt uses now.
We’re talking about TVDB which the deleted shows are still on.
And that link says if it’s uploaded to their own YouTube channel it may be allowed anyway.
Bumping because I’d like an actual answer. This isn’t the first time this happened. So should I expect series to randomly be removed every couple months?