I have my music organized as follows:
In Folder Hierachy view, about half my Genre folders don't have images. All of the other folders within have images and there are no missing artwork on my tracks.
I have tried full rescan, clearing the cache/data, uninstalling and reinstalling the app and changing the order I select folders and cannot get images to appear.
My music is split between my 500gb SD card and then my phone storage. I'm on a Samsung Galaxy S10+, running Android 10. Poweramp version is latest from the Play Store.