[SOLVED] Email notification settings don't stick

Troubleshooting
4

I had the same issue but it was fixed by specifying Docker image version.

services:
  mattermost:
    image: mattermost/mattermost-prod-app:3.9.0

I found image size is different between 3.9.0 and latest. The latest may be unstable.
https://hub.docker.com/r/mattermost/mattermost-prod-app/tags/