As you seem to be Alexander Borsuk...

Why the removal of the MIT license?

Was that decision put to a vote like "all important project decisions" are? I assume it can't have been unless Roman is blatantly lying about only noticing it a few days later.

Removing the MIT license from the repository and claiming it as 'my code' is not how open source works.

It's sound like the person who removed the licence also originally wrote the code, and just didn't intend to add the MIT licence to it?

Though luck. Be more careful next time. That's how licences work (not only open source ones, or software ones).

Nope, Roman has actively contributed to this MIT-licensed code since its inception in 2021.

Yeah I mean, of course technically that's not how it's supposed to be done, but if they initially added the code and the licence (the latter by mistake), then I can see how the internal narrative is "here's my code (that Roman has contributed to) and I accidentally added the licence to it - oops, let me remove that before we accidentally make it public".

Of course at that point they should have realised that they weren't the only author of the code any more and that Roman understandably would have the wrong idea. But I see how it's an easy mistake to make, and it would probably also have easily been resolved had Roman reached out about it, rather than just instantly making it public and implying nefarious behaviour ("quietly made a change...discovered by me").

How come the server code was (is?) de-facto closed source and this fact was kept hidden?

In a project that claims to be open-source, privacy-focused and community-driven.