Lightroom Classic 8: RAW->DNG only converting SOME photos

I’m using Lightroom Classic CC 8.0. I have a library with 75,427 photos in it, which are a combination of .NEF, .ARW, other files (.TIF, .jpg,.png, etc), and now .DNG.

I selected every file in the library, told it to convert them all to DNG (and delete the original when done and all that jazz).

However, it seems to skip a lot of the photos.

The progress bar is almost done with its 24-hour processing of this task, and when I look in the masters directory I see 26,832 DNG files and 31,692 NEF files. BS it’s almost done.

I’ve done this on smaller scales too: I’ll select one directory, tell it to convert them to DNG, and it’ll convert half of them. If I do it again on the same directory, I’ll get more. After a couple passes it’ll finally convert them all.

Why doesn’t it actually convert them all and how do I get it to do it the first time?