Here are my preferences, I have not looked at those in ages. I assume, based on the information in this thread, that the "People, places and content I'm following" setting being set to 'All activity' is what is responsible for these notifications that suddenly appeared.
I'll change this to 'Never' and then follow my desired communities again and that will probably take care of it and return the prior behavior of this forum?
Again, thanks for your help!