[com.bigduckgames.flowshapes] microG crashes after Play Games sign-in

Affected app
Name: Flow Free: Shapes
Package id: com.bigduckgames.flowshapes

Describe the bug
Upon launching the game, it automatically picks up my Play Games account (I see a "welcome back" popup from microG about it) and after a few seconds I get a "Unfortunately, microG Services has stopped" message. If I stay in the game, this repeats indefinitely. "Allow Play Games account registration" is on in microG settings.

System
Android Version: 6.0.1
Custom ROM: this is not a custom ROM, this is TouchWiz on Galaxy J1 mini prime patched with Haystack

microG
microG Core version: 0.3.11.250932
microG Self-Check results: all ticked

Additional context
This is an upgrade from an older microG version, but I haven't played anything that used Play Games before now. I did try clearing microG Services' data and the game's data and rebooting, that didn't help. Curiously, this all was happening even with "allow Play Games account registration" off (yes, it still had been signing in automatically). I didn't even know the feature to toggle registration existed until I went to explore microG settings :D

No source file, test, stack trace, or entry point is named in the report. Start by reproducing the Play Games sign-in flow on Android 6.0.1 with the listed microG version and capture the crash details; done means identifying and fixing the cause of the repeated microG Services crash and verifying sign-in no longer triggers it.