JetBrains TeamCity CI stopped sending merge requests triggers

I had this setup for half of a year and it worked flawlessly.
But starting from 2nd of April I have problems with it. Gitlab does not send MR events to my TC server.
I have only “Merge Request” trigger enabled.

How do I reproduce:

  1. create feature branch
  2. create merge request of this branch into develop branch
  3. Nothing happens

Expected results - TC pipeline is started.

When I activate push triggers - it starts working. But this solution is not acceptable.
When I push “Test settings button” - TC pipeline is started.

My TC is behind reverse proxy, so I also checked logs of it. When I use push trigger and “test settings” button - I see connections from gitlab addresses to my TC.
But when merge request trigger should be activated - there is no connection from gitlab addresses.

I did not find any information how to debug it from gitlab’s side.
Help please?