Wow, am I lucky I did this at home! I would have seen my @s$ at the gig later.
@peter please check Playlist File save / restore in v3.5.6.
I prepared my playlists on my home iPad Pro, then saved them to OneDrive.
I could not restore them to my gig iPad.
I was able to Airdrop them from one iPad to another. That worked! (At my gig I wouldn't have had the other iPad to do the Airdrop. Phew, for doing this at home!)
I am NOT able to save a playlist to either OneDrive or iCloud and then try to load that file into v3.5.6 on the other iPad. I get this error:

(The files are .stpl files at around 329 bytes for 13 or so songs.)