You have to be patient, the developers do a selfless job that we all appreciate. I know it is sometimes frustrating when it comes to a major failure. The last days whatsapp and signal notifications arrived sharp (very rare), but with signal I have always had a problem, you call a person and you get a tone but the other person's phone doesn't ring, it also happens with WhatsApp, but that already happened to me with stock android.
Regarding tutanota, you can't blame graphene, as I told you many friends use their service, we all have problems with notifications from time to time, this failure occurs with both google stock and graphene, so we can't blame graphene . The thing about tutanota is worrying because if you don't enter it manually, you can have emails that arrived days ago and they use their own daemon to avoid push, little by little they are improving it but it still has quite a few bugs or deficiencies. In this case you can get angry because many users are subscription users and failures take a long time.