On my pixel whenever I use the pull to right gesture to go back on a post the background will be black. However, if I use the back button or system back gesture the background shows the previous screen.
On my tab both gestures show the previous screen, so it’s not a general thing I guess…
I have the same behavior even with Sync for Reddit since some security android update in a custom ROM… Hopefully this will be “fixed” on the android side again.