The SD Card should NEVER be formatted as "Expand Internal Memory"
Only format the SD Card as "Removable Storage"
Android just handles SD Card management terribly and reviewing the Google boards it appears no one is interested in solving this.
A huge number of DMD2 users formatted their SD Cards as "Expand Internal Memory" and then also enabled the "Use SD Card for Storage" option under the DMD2 General Settings.   However, this "Use SD Card for Storage" option is only for SD Cards formatted as "Removable Storage".
If you need to reset the DMD2 app and SD Card you can follow these steps:
https://youtu.be/ZtDapQIYODI