The only log available would be the webserver access log, where you could see if the submit is actually getting to the webserver.
This may end up needing an advanced support ticket, since it sounds like it's going to involve some debugging.
If you're comfortable with code, debugging usually involves tracking down where it's hanging, so you'd add some code that prints out a message and then exits at certain points. You'd keep moving that code down in the script until you can no longer see the message, and you'll know where it's dieing.
