I am afraid there is not much we can do for you on this forum. I highly suggest you contact Mendix Support for this. Hopefully they can resolve this issue for you. Good luck!
I don't know if it's what's causing your issue but it's worth trying: are you doing your test in an incognito window with all extensions disabled? That would make sure none of your extensions or cookies are interfering with the test.
I took the test last week, i had the same problem. I realised that i was clicking through the question really fast and that cause a problem.
Also another problem i noticed is that the test got disconnect several time and you have to go thourgh all verification process when you resume it, I willl suggest to contact support or write it to firstname.lastname@example.org
They already record test so there shouldn’t be any problem in getting a new link for reattempt