Interesting. Hum.. because there is not Google Services, i also don't get the crash reports from you.. gotta figure out how to see what's happening.
Discussion
I am not sure the cause. You should look for alternative to Google APIs in the future to support degoogled android.
Many apps, like Signal, have developed alternative solutions to things like push notifications when Google APIs are not found.
There's also https://unifiedpush.org/ so you don't have to roll your own push notification library.
This is the way.
unified push is dev-friendly, cross-platform, awesome non-FCM push notifications. Sample android app integration on their github here: https://github.com/UnifiedPush/android-example
test (sorry!)