Music files not transferred during upgrade to new device..

I’ve just upgraded from an iPad mini 5 to the latest iPad Pro and went through the sync process perfectly, except for two mp3 files that were stored in the files folder of the previous iPad’s music app. They are missing from the new iPad but are listed in the playlists. They play fine on the previous iPad. If I try to play them on the new iPad I get told that they’re not available in my area. If I select share on the old iPad then I get told that they can’t be shared. Any idea how to transfer them?