Galaxy S8 update to Pie - Doggcatcher stops playing after screen locks

This is the second issue Doggcatcher seems to have since my S8 updated to Android Pie.

Now when the screen locks, podcasts stop playing. If I shut the screen off manually byu pressing the power button, audio keeps playing for one minute, then stops.
If I keep the screen awake, by scrolling around in another app for a few minutes, it continues to play. Then if I leave it alone then the screen will eventually shut off as normal, and one minute later, it stops playing.

As soon as I hit the power button to wake the screen up, play starts again. But if I do nothing else and let the phone re-lock itself, audio stops again.

For fun I tried changing the advanced setting to "keep alive always" but it doesn't make a difference.

I never once had this problem under Oreo. I also don't have this problem with my audiobook player.

I checked the list of apps I set to not allow running in the background, and Doggcatcher is not listed. I have power savings set to "optimized", which is the second most generous option - though it says that only applies to screen brightness and quality, so it shouldn't matter.