Have you tried logging out of the app in settings? I don't mean exiting the app, or closing it, or uninstalling it.
Settings is gear icon; you might have to scroll down on the left to see & click on log out button.

I use both pc and app, and do not have issues with it auto assigning if I have logged out from the app itself. I have tried this on several teams and for varying lengths of time between desktop and app, and when I go back to desktop the points accrue and stay until I assign them.