P: JPEG File Export to DNG Disables Import Module & Synchronize Folder Functions

Question which comes up to me immediately : Why would you EVER export / convert a jpeg to DNG???

Thanks Rikk. I forgot to add the Export module screenshot with the settings that exhibit the issue. Any other ideas? Are there any other "settings" files associated with the Export module that could be causing the issue? I'm guessing not too many people export JPEGs to DNG file format and this may only be happening on certain systems (race-condition).

In Preferences> General> Completion Sounds I have Asterisk assigned to "When finished importing photos play." A normal Export operation sounds an Asterisk alert when the taskbar activity closes and then a second Asterisk alert sound after a slight delay.With the failing JEPG to DNG Export I only hear a single Asterisk alert sound, which probably indicates the Catalog file update to add the new DNG file fails.
Update: I just created a new catalog with 10 raw + JPEG image files and the JPEG to DNG Export issue persists. Weird!

I tried to repro on 10.14.3 and Win 10 1803 and it is working for me, Todd. 

I can export a JPEG as DNG with Add to Catalog checked
and 
I can export a JPEG as DNG with Add to Catalog unchecked. In this case, navigating to the folder and hitting the Synchronize folder option does find and allow for the import of the file.  

It seems to work the same whether or not I have the Add to Stack box checked.