[vanos]

This problem has happened to me several times.
Have you tried opening the other page in a new browser tab, and the original ISTA browser tab remains intact? Will the connection with the Backend server be interrupted in this case as well?

I have seen issues when running a test plan if you navigate away from the "ISTA Workshop" page on the website whilst ISTA is open, it seems to kill the backend connection to the session & cause the rest of the programming plan to fail.
I found this when trying to obtain the control unit validation file, I had to cancel the validation part of the test plan then finishing the concluding tasks, then create a new plan to obtion the validation file, go to the website to obtain the response file & then start a new session to load that file into the car.