"Save Online" with custom audio sometimes doesn't upload any audio

This is a bug that has happened to me 50% of the time when trying to upload certain scores (large ones involving multiple soundfonts and tweaked effect settings like those below).

The score will export and upload like normal, or at least seemingly. But no sound will be produced when listened to on musescore.com - and sometimes the play header will advance, and other times it will flicker but remain unchanged.
One of the telltale signs that this has happened is that the uploading portion of the uploading process will happen remarkably quickly, like it didn't even process anything.
It's possible that this is a problem with musescore.com, but I'm creating an issue here as well in case it's a problem with the program.