@Nobody, I've had the same problem for a while now. I have never got to the bottom of it.
Just like you, it behaves as if there are no replay gain tags to be found. I've verified them in other players (Audacious, DeaDBeeF) and command line tag utilities, they are there.
Some of the help I've seen suggests that it is a gstreamer issue, but I don't even have gstreamer as an engine option on mine (Version 1.2.7), it's using "Plays to a Pulse Audio Server" (I'm using pipewire for sound).
I'm about to give up and find another player. Pity, I quite like the interface, especially the lyric finder works quite well for me.