@notpeter I'm actually still seeing the same error, even with your latest version (1.1.2). I was able to fix the issue by unzipping and rezipping the PDX folder.
I had the same problem with another game, that was resolved with the same method. However important to note that the dev said they were on Windows 
Is this maybe a bug with how the Playdate (or the sideload server) unzips archives?
EDIT: erp, I think the bug I'm seeing is related to the discussion you linked above but I suppose its still worth mentioning here.