This seems to be an iPhone or mobile app issue:
There are times when I'll get a notification on the PM app on my iPhone, and even after tapping on it and reading the notification, the red number doesn't go away, and new notifications don't show. If I move over to the desktop, the problem isn't there. Eventually, it clears, but I have no idea how or why it clears. I've cleared the cache on my phone, to no avail.
Any ideas?

There are times when I'll get a notification on the PM app on my iPhone, and even after tapping on it and reading the notification, the red number doesn't go away, and new notifications don't show. If I move over to the desktop, the problem isn't there. Eventually, it clears, but I have no idea how or why it clears. I've cleared the cache on my phone, to no avail.
Any ideas?
