That looks like a problem from the server side, the token is invalidated when you enter that activity. The latest version of the app is 3.9.2, you can try to update it to see if anything changes, but it seems to be related with some configuration on the Moodle site.
It may be related with the token being used too much if the app is making a lot of requests. If you have admin rights you could try removing them to see at which point it stops working. I know it's tedious but nothing else comes to mind.
If you want you can invite me to that course and I can log in to look at the network requests, you can invite me using the email
noel at moodle dot com.