That's an error that used to occur a lot with the Submit page, and it has nothing to do with "loading the page with missing parameters"--in fact, the reason those drop-down menus work is because that's what the page is designed to load when it doesn't have all parameters.
I don't have the specifics on how the Submit page's bug was resolved, so all I can offer is a user-side solution. Whenever you get the white page, hit F5 and go back to Matchups and you can continue on normally.