If you use Bridge, it is considered to be good practice to set your Prefs. to "Compact the Cache" each time that you Quit out of Br.
Lr has a similar option regarding its Catalogue. Compacting removes links to old files which no longer exist.
If your Converter software is running really slowly, you might need to delete your Cache manually, and start from Scratch again, but you would then have to wait while all your Thumbnails get rebuilt when you open a new folder.
Thank you, guys, for all the suggestions. I will try these viewers...
Just downloaded the "Faststone", free for home use. Seems pretty fast!
I love Nikon cameras and the Z7 is great, but Nikon is not a software powerhouse. Unfortunately, today, hardware and software must work hand-in-hand to make the product usable...
I'm running an i7 Skylake with 64 gb RAM and a SSD scratch disk and my D850 files are a little slow in View NX. The D5, D500 and D810 files fly pretty good. The more images on the card, the slower it goes until all the thumbnails are downloaded, then speed is pretty good.
I started using the FireStone.... FireStone is definitely faster than Nikon ViewNX by the order of magnitude.
But I cannot see the lens exposure data, like I see in the View NX. Also, is there any way to grade the picture in the FireStone, like 1-10 stars?