During this time, when everyone is working remotely, here are some ideas that I think would make a huge difference.
The conversation bubble - it should be blue when you have a new unread comment and gray when you already read the comment. This way someone can just look at a board and see everything new for them.
Inbox - replies when you are tagged should be listed there, NOT just the first time that you are tagged ( I heard that you are working on this)
Have a number showing you the updates that you have not read on the side bar for each board. Obviously somehow you have to be able to click on the number and the pulses come up. Something like the below image.