See #185022
I still have this bug, although I have updated Rhythmbox (3.5.0) and libpeas (1.38.1) to todays version.
It’s not a bug and is detailed in my response in that thread. As far as I know, nothing has changed since then. Maybe try the Flatpak version.
So if I understood correctly, python-gobject is breaking some apps. In that sense it would be a bug?
Unfortunately Flatpak is not an option, but I hope, there will come a solution to be able to use plugins again in rhythmbox 
So in case, the discussion is continued here:
I am going to close it here. Thanks for the info @Yochanan .