Hi Aldevinas,
Parallel maintenance is a technique used to avoid blocking threads during operations that require going through a large number of records. For instance, imagine you need to loop through all invoices but only want to update a few of them. In this case, the invoices that require updating would be processed in a separate function that is called as qupdating. This way, the other threads can continue executing without being blocked, and users won't experience any performance issues. However, if the main thread is blocked for a significant amount of time, users might see the message you described.
Unfortunately, in your case, the best solution is to run the maintenance during off-hours, such as overnight, to avoid impacting users' experience.
I hope this cleared it out, let me know if you have any additional questions.
Best Regards,
David D.