Conversion just stops

I tried (several times) to have a bunch of about 40 images converted by NLP.
Every time, NLP simply stopped progressing and went back to its initial “convert” state.

The files in question were .dng files created by DxO software that I used for its optical corrections and excellent noise reduction. File sizes were between 50 and 100+ MB each. (on macOS Mojave on iMac 2019)