So, in my third year of Uni or even my masters I remember one of the 'cool' professors telling us that the late submission deadline only applies an hour (may be more may be less can't remember specifics) and that you wont be penalized if you submitted a few mins late, I don't know if that't true but he was a senior lecturer within the university. During Covid all my tests and assignments were online and during second year, when everyone in the module (70+ students) tried submitting their test at the same time, the system crashed, and wouldn't allow people to submit the test for 2 mins before the deadline, and then only allowed us to submit after the deadline, but it also prevented you from submitting.
The university accepted everyone's late submission if they showed evidence of them attempting to submit 2 or 1 min before the deadline.
However, in instances such as yours, the Uni could be ***** and say you should have converted it way before the deadline or used a univeristy computer blah blah. But I think they may be lenient, it was after all a system error and not you being lazy and forgetting about the deadline.