Disk Activity at Largest Buffer Setting

When playing any project even if it’s just an empty track with no audio, the disk activity meter starts bouncing around like crazy when I go to the largest buffer setting (4096). Every other buffer setting including 32 is totally fine. Anyone else experience this? I’m using an RME HDSP 9652 with the latest drives and Windows 10. This happens in Cubase 9 but not in 8.5.