This sounds like a problem that wouldn’t have existed in the first place if following a binary protocol with a standard format and using a proper serialization library.
The issue comes from CSV files looking easy to generate by hand, when it in fact is not.
This is a decent point, but practically the platform uses some library in their ancient ASP application. The issue is that these types of things can't be fixed because the original author is gone and the tech debt has become unmanageable. This is not the only issue we've had, unfortunately.
Debugging this same issue in a binary format is far and away not going to happen in this scenario.
...but if it was a binary protocol that did have a problem, of any sort whatsoever, and you couldn't get the provider to address is (in time), then you're hosed if it's not human readable.
The issue comes from CSV files looking easy to generate by hand, when it in fact is not.