Anytime a person has issues, please give us feedback via the call feedback dialog. This helps us pin point when the issues occurred we can go through the error logs.
Make sure your application is up to date. You can do that by going to the menu bar. Click on Tandem, then check for updates.
While annoying, you can ask everyone involved to quit and open Tandem again. This will solves most of issues were things get out of sync.
If #2 didn't work and the same exact problem persists. That's great, because it means we can reproduce it. In that case, please send us what are you doing to trigger the issue and we'll fix it super fast (trying to reproduce an issue is 90% of the battle, so if you can write it down, we can fix it in no time)
Finally, if you and your teammates have done all the above and it's still not clear what's going on, then please give us as much detail on the issue. Even better, record a quick video (you can use https://recordscreen.io for that)