There isn’t a great excuse for it anymore, as Canvas (or your favorite other LMS) has a big button pre and post submit that will show your document as it appears for the teacher.

Obviously at this point you’d explain quantum bit flips and point out how absurd their policy is. :)

I'd be curious to know what the natural rate of docx corruption is, and what the sources are. What are the odds of cosmic rays flipping a meaningful bit right as the docx is written to disk but not before, and in a way that doesn't cause a crash? What are the actual error modes with both spinning and solid state disks, across a variety of filesystem types and usage patterns? Is the damage normally like one bit, or a would it normally flip a few in some (physically) localized region?

(It's just not something I think about very often, and only now do I realize how useless my knowledge is! I could speculate based on the flux of high-energy particles and the layout and energies involved in various storage media. I would expect the energies on non-volatile storage to be much higher than volatile storage, and so for bit flips to be rare. I would expect flips to be singular, and not come in groups - but if they did it would be temporal, not spatial - something like a solar flare. The interesting flips would be the least likely ones, where the serialization code is running. The threat-model here is the relatively large memory region consisting of the union of something like [cpu, kernel, jvm, thread, bytecode]. That's quite a surface area, and while it's fun to speculate about what a bit flip could do at various interesting points, but I assume for simplicity they all just crash your code. (I wonder how often random bit flips are why restarting software is unreasonably effective at fixing problems - or is it just an epidemic of thoughtless race conditions as I've always assumed?)

Conferences are aware of it too! At least one major conference requires you to either upload your documents at the deadline, or a cryptographic hash of your documents, which can be submitted up to a week later. That way, they mitigate the load from the thundering herd of last minute submissions, and thereby avoid the inevitable excuse that the submission server died or that the internet was too clogged to upload their gargantuan video figure by the deadline.