Indesign auto-updated during the course of the evening and NOW will not render variable concept fonts to PDF. In particular, I had a problem with Acumin Variable, across an ENTIRE magazine. For clarity: It appears on screen correclty, it renders to ping correctly, but does NOT render to PDF at all (all the custom variable lose their settings.
There are still some glitches in terms of how PDF is generated when these fonts are referenced, especially if you try to manipulate the PDF files after they are created. If you are going to try using these [concept] fonts, make sure you do so with the latest version of InDesign (i.e., nothing prior to 16.0). Since the variable font names are different than the non-variable names, the chances for conflicts are relatively low.