Thank you for your reply @LeonidS

Dolphin worked on a shared server, really very well, I've been using it since 2007. The problem started when I moved to a VPS. I wanted UNA on a VPS (6 CPU Cores, 16 GB RAM, 400 GB SSD). I moved dolphin with the content to a VPS and installed UNA to migrate the data. Dolphin did not work with permalinks even on the VPS server, so I turned them off. That didn't help either. After that I ran both dolphin and UNA on localhost and transferred the data, everything works perfectly. I transfer the UNA with all the data to the VPS and it doesn't work again.

The problem is the same as in the post you mentioned, only I can't solve it that way on a VPS server.