Same thing happened to me -- I did the same thing (deleting apps and trying again). Mine worked after I restarted my computer then went into preferences and deleted a few old/larger files. Hope this helps!
2019 MacBook Pro user, they made me download and run chrome to take the exam, last time (July-flex for me) they let me use Firefox. I am not sure if that's even a choice now, so have Chrome as an option just in case!