Revising the music on a USB drive for my long Saturday trip, I discoverd a number of repeated tracks. I had wondered why one particular album of 14 tracks was repeat playing when that feature was turned off. It had both mp3 & aac formatted files, the reason being that I’d burned some mp3 CDs and had to use iTunes to convert them from the original aac.
The exporting from iTines to the USB drive was done with an app called ITuneMyWalkman or ITMW, it's an old thing that predates iPhones and still works quite happily under High Sierra.