While I admit that this could be a Telegram problem, I really don't think it is.
I have one contact from whom I don't receive any notifications for text, audio or video contact on Telegram. I first thought it had to be some setting as IG was only him, his mother could send at nearly the same time and I got the buzz.
I first tried reinstalling the app, provided no change.
I then removed data and chache, removed thevapp and restarted. I then installed Telegram FOSS. Same problem.
What have I missed?