Thank you very much for your tutorial, all the problems are now fixed!
I think you might need to update the Jam Export URL as well (here and on the jam entry page).
I don't see anything when I clicked Soundfonts button in Jam Mode, and I think you mentioned you were using a custom tambourine SoundFont?
(If you're not doing that anymore and just using the default sounds instead, that's cool too)
but let me know if it's the case if you are using a custom SoundFont and forgot to update the URL - I'm hoping that's the case.
Otherwise this is a bug that I will need to fix.