It's because they didn't bother to certify the latest hotfix (ZYBF), so the phone only passes basic play integrity checks and not the strong or hardware backed integrity required for more secure apps. This is the same reason Google wallet and such have stopped working. Really annoying as the previous beta was certified but the hotfix isn't.
I already had the app installed prior to updating and it still works (the play store just prevents me from updating it), so you should be able to sideload it worst case
