This has always been an issue when adding dmdext to a front end. The process doesn't close out, and when you reopen it again, NADA.
just add this to a txt
taskkill /F /IM dmdext.exe
and change the extension to .bat
use that file as your launch after...you can do the same with autohotkey, which is what i used i even added a slight pause then ran the taskill command again, to ensure it was closed out.
If you want to avoid FX3 breaking your setup, just back up your fx3 folder in steam, or make the folder read only.