Hi Lee,

My apologies, now I understand what your problem is.
Please make sure that your reports are multi-threaded by going to System > Settings > Optional Features > Performance > Parallel Reports: Multi Thread. Also make sure to 8 into Report Slots value.

NOTE: Restart the server after applying changes.

This will ensure that you have enough slots for running reports on other threads which will eventually lead to you being able to run maintenances uninterrupted.

Please let me know if this helped.

Best Regards,

David D.