I agree that the "cleanup invalid sessions" option helps. We have never needed this option in the past. Enabling this new option does seem to resolve the immediate problem but does not address the root issue. The cryptic "Invalid map(K, T)" error needs to be explained by FSLogix.
My biggest concern here is that the FSLogix group pushes this thought that "Customers are required to run the latest version" (in principle); yet, the FSLogix group is completely silent when legitimate issues are encountered.
There should be a public acknowledgement of the issue and an explanation as to what it means and what (if anything) can/should be done. Instead we just have this glowing announcement that this new version is great and everyone should upgrade. Hate to be critical here but I don't think this situation is good.