not sure if my comment can help. On my MotoG4+ I have
- eOS : e-0.7-n-2019111931239-dev
- ProtonMail : 1.12.2 (680) installed from Apps
and everything is working well.
For those who were having issues with Protonmail app - pl can you test with the latest builds for your device. The latest builds should have MicroG version v0.2.10.19420. This should resolve the notification issue as well.