UPDATE: now it works. I didn't change anything. I just had to wait. I use latest version of everything, I was sure problem is on TestFlight side

thank you. this should be the accepted answer (+ of course clean and build)

I've just created external group for testing and added myself and it's working for me too. Thanks.

it's not related to just One Signal. I don't use it and have this problem. My app only contains widget extensions