MacOS High Sierra Messages app unread icon reappearing, causing system to hang I am experiencing a strange problem with the inbuilt messages app on my iMac. For 2 of the threads in the app, the unread count is not resetting and when I read the thread, the blue unread icon initially disappears before immediately reappearing again. Furthermore, doing this seems to cause the rest of the system to hang for some time afterwards, so it's becoming quite problematic. I have tried the following to fix this problem:


Force quitting the app.
Deleting the threads (problem reappeared on next communication with the person in question).
killall Dock in Terminal.
Booting in safe mode.
Changing notification settings.
Scrolling far back through the threads.
Reinstalling OS (not a complete clean reinstall).


None of these things have worked and I'm now at a loss for what else to try. Has anyone seen this issue before?
I think the solution can be found in DeerSteak's answer from: https://apple.stackexchange.com/a/332311/100302


Quit Messages.app
Open a Terminal and:

cd ~/Library/Messages/Archive

Search for the stuck message (compare timestamp) e.g.

find . -iname 'annoying person*.ichat'

Once you've located the offender, delete it
Restart the Dock

killall Dock