Windows 10 pro (OS Build 16299.192) with the latest version of CIS.
i downloaded and installed defraggler, and when i used it to analyse all my drives, it appeared to initiate a full realtime scan of the entire drives in the same order they were analyzed in. (Checked this with resource monitor) At the end of each drive scan, it wrote large amounts of data to my C drive.
It also would scan each file as it was being accessed during defrag. adding defraggler.exe and defraggler64.exe to application exceptions appears to resolve the issue, but this seems like strange behavior.