Barion Payment interview questions

Started off with a relaxed atmosphere and casual interviews. There were two rounds of video calls which were a good time, but things derailed after this. After two tech rounds I was leaning towards accepting an offer (the challenges described meshed well with my experience, and this is a well-funded company with good opportunities ahead of it), and was invited to a meet at the office. I assumed this will be when I get an official offer, followed up by the usual HR talks and paperwork. It ended up being a sort of a casual team fit meeting, not as discussed, but I went with it. So a total of three rounds. I was supposed to start ASAP (they asked for this), but was not contacted by HR. Instead, I exchanged calls and mails with someone who signed as a product owner, but later said they were a hiring manager. I did not see any paperwork, and a few days before the agreed on starting date I got a notice from the authorities telling me my insurance status changed - without me ever seeing an official offer, a contract, or ever agreeing on anything other than me waiting for an official offer and something to sign. I eventually got the backdated(!), unsigned contract one day before my proposed starting date - after asking for it (!) - along with chains of emails that suggested that HR assumed everything was in the clear, and had a draft ready 5 days before I saw it. When I confronted my contact with this, I got no clear answers, just deflection. This is a gray area *at best* according to local legislation. I was never contacted by anyone other than him after this situation, despite repeatedly asking for HR. The contract I eventually received was for a different position than advertised (Sr. Software Engineer), missed a major benefit that was advertised for the job (private healthcare), had a lot of unusually strict clauses, and was overall not something I would've signed. This all came as a surprise, given that the product is fully legit and somewhat well-known locally, but all signs were pointing towards org issues, and a bit of a dev limbo situation. Not unusual, but usually comes with a better package than what was advertised.