Actually I think it is the same bug as REQ: Feed improvements [Search & stability]
If I click on any shared files the event where they were first added to Gdrive gets put at the end of the feed log despite it being 6 years ago and despite it being before it was shared with me. Because the files were added by somebody else it feels the need to notify me. But just as it shouldn’t show ancient history in the log before it shows all the events before it doesn’t make sense to notify events that are years old.
The only mystery is why it notified me about files I hadn’t looked at but something weird has happened to them today. They have disappeared from the Gdrive “Shared with me” page but I can still find them with a search. One is in my “Suggested” list and if I right click and select “Show location” the Drive web page locks up.
Perhaps the originator has deleted them but Drive can still find them with a search.