Another bump here, I am afraid. A constant 30MB/sec with 18.8.2356 (build 18.8.4084.0). I ran and uploaded the report with your support tool. Hope it helps.
...although ... it IS possible that the "Resource Monitor" is not reporting accurately. Just because it says that my disk is constantly writing 30-50MB/sec doesn't mean that it is. First note is that I/O Priority is background. Second (and important) note is that "Task Manager" does NOT report the same number. Task Manager reports nominally 0%, I see Avast show 0.1-0.2 MB/sec occasionally. And for about 5 seconds every 30 seconds it says that System is running at a few hundred MB/sec.
So I don't think the lscache.dat writing is constant. It bursts foevery 30 seconds.
I turned off transient caching in the file shield and it did NOT fix the problem, including after reboot.