Possibly related, just prior to the 4.0.0 update, the feature flag '"boolean name=“android_notifications_grouping” had a status change from ‘false’ to ‘true’ and I also experienced the same notifications disabled issue. They’ve been fine since re-enabling after I noticed it when updated to 4.0.0
This doesn’t explain why iOS has the same issue though.
And my biometric settings always reset to ‘off’ after every update. I’ve got used to automatically re-enabling them again after updating.