It turned out to be a BAD Micro SD card adapter.
I've successfully used this one before but it just failed to allow syncing to a 128G card. It synced fine on an 8G card. MM could see the card, the files and the folders but the option to > Right-Click a playlist and Sync to a Drive Letter was not showing in the menu. Finally when switching to a different MSD card adapter which then fits into a USB3 adapter, the Sync option miraculously appeared. Android even located the Playlists within 10 minutes.