I know this is very old post. But I will try my luck anyway. I was wondering if anyone knows that was the solution?
I had this problem. It would happen a dozen times a day on all of the clients. The screen would go a pinkish colour with the error description you described above and it would have a logout button on the pop up.
I had the system integrator at my site and he spoke to someone at Inductive Automation who went online and looked at my system. I am not a database person and it was a couple of years ago so my recollection is a little vague but he found the “database indexing” was wrong. He did something to my database, added an extra field or something and it has not happened since.
Hope this helps.