Drashna, as you know I've been struggling with the memleak issue so much that I considered switching to Storage Spaces.
However, that product is quite confusing so I asked on the datahoarder subreddit and a user (that sounds knowledgeable) suggested that REFS might be the leak.
And...this did start happening on/about the same time I converted to REFS.
I'm going to remove each REFS drive individually and then readd as NTFS drives and report back to see if that's the issue.
Here's the link.