Many errors: "You can't view the same activity on two browser sessions."

Summary

Many users report this error, when resuming a training. Cache cleaning workaround.

Content

Hello,

we have been live for a few months and the platform is stable now, but we have got a few dozens people reporting that they cannot resume a training due to an error:

"You can't view the same activity on two browser sessions."

They do make sure they have only one browser opened. In fact, rebooting their whole PC doesn't change anything.

What does work is to clean their browser cache.

At least one user reports that the issue occurred after using the "back" button of the browser. Does the code take this case into account?