Hi Aljaz,
The log does not contain another distinct error or failure cause besides the user being blocked or inactive.
But,
(com.mendix.modules.queue.Task
and com.mendix.modules.queue.MicroflowTask
and java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source))
it clearly shows that this user validation failure happened when an asynchronous task or microflow was trying to start by establishing the necessary user context within the Mendix Runtime's Task Queue.
If you find a solution to this issue, please post it in the comments.
Regards
Guna