Ok, I'm going to be most unhelpful here to report that that the folder that has the mix of files types contains raw .nef files from various Nikon cameras I've had over the years. A D90, D7000, D7100, D800, D800e, and D810. The system is an x64 version of Windows 10. I am running an AMD processor with 8 threads and 4 cores and when I open the program that is the number of cores and threads shown.
Only because of the tine that Mike replied (just a few hours ago) I will interject a comment and you can try this until Mike gets back to work here.
The Nikons produce 75 mb raw files. These take a huge amount of time to process compared to either of my Canon camera; one at 7 mb and the other at 13mb.
My suggestion is to wait when it says please wait. Sometimes Task Manager says not responding, but it is working inside.
Try creating a folder of 50 NEFS and see what it does.
Remember this cache build is a one time thing.
Fred