Ok, just updated to 1.11.0 (latest app store release at the time of writing) and it behaves exactly the same. The icon changed after updating, however, subsequent attempts to change it are ineffective as before, even if the app is swiped up from the task selector to “kill” it. It seems like swiping up doesn’t really kill the app, however, installing/reinstalling/updating from the app store does.
To test this, I’ll try offloading the app (delete app but not app data) and reinstalling to see if my hypothesis about updating/reinstalling is correct.