Assume that you have an Always On Availability Group (AG) in SQL Server 2017. When you process a read query and use a parallel redo thread instead of a single redo thread for dirty pages on a secondary replica, the performance is slow.
This issue occurs because of contention between the read query and the redo thread, and because the table is locked.
To work around this issue, use a single redo thread instead of a parallel redo thread.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.