That's probably it. You need AML to make them work together.
Just search "DDPlus" and "dolby" on setting on your phone - apps and notification - then clear storage, force stop, deny acces storage, and then disable it. Do it on DDPlus first, then dolby (system app)
After that, allow acces storage, and enable the the "Dolby" first, then "DDPlus" (just like refresh)
Open the app again and again.
*Sorry bad english, hope working.
But have u installed the audio modification library on magisk?
AML is Audio Modification Library. It can be found in Magisk downloads. Remove your installed audio mod modules, reboot, then flash in this order: DDP, V4A, Audio Compatibility Patch (Optional) then AML.