Yeah, this occurs on phones with Android Oreo and up (which your Pixel phone is), and I think the November or October security patch forced ALL icons on my pixel to go to the new adaptive icons format.
The developers of BeyondPod could fix this by creating an orange mask with the BP logo in white in the middle (eliminating the white mask), but shit they can't even fix the bugs that have exited for months so I doubt we'll see any visual improvements.