NAS in Btrfs RAID1 - one drive is at 250mbps R and 0 W, other is at 0 r/w

I am trying to figure out what is happening with my drives and why are they being at a constant use. Right now one drive is at maximum reading speed and 0 writing speed while second drive is at 0 for both reading and writing. Defragrament and Scrubbing has never been ran and are not running right now. Process monitor shows nothing. LAN utilization is basically 0. What is happening? Is this some sort of weird Btrfs balancing thing? I feel that I am going crazy! If this is important, NAS is Asustor Drivestor 4 pro gen2