To clarify where I’ve had issues:
There are many messages (DM) that I never received notifications for. This was rampant for a while, happening routinely.
I am subscribed to two forums and for a long time (months) was not receiving all notifications. I have a friend who had the same problem for a forum she started. I would sometimes receive notifications when she wouldn’t .
I have run across responses to my comments on the feeds that I never received notifications for.
And lately whenever making a post in feeds, submitting a message in DMs, or making a comment on a feeds post I receive error messages. “Not found” being one of them.
In the past week the lack of DM notifications hasn’t been a problem for me but it was a consistent problem for at least two months. The people I regularly message with were having the same problem.