The actual bug tickets etc are public. There is a report that's been published into what happened that goes into a lot of detail on each individual failure. In most cases they figured out what was wrong. The requirements for the system was kind of a programmers worst nightmare tbh - they needed a very complex and frequently changing database app to be usable offline, so they had to implement a lot of sync and conflict reconciliation logic that frequently turned out to be buggy or have race conditions.

They also had incredibly awkward bugs like "the touch screen hardware we deployed had a bad manufacturing batch that caused a subset to start submitting random button presses 12 months after deployment". It took them a while to realize that the actions weren't genuinely being made by the post masters, etc.

And yeah, iirc they lied to the court. Courts are supposed to anticipate this of course, but unfortunately defense teams near universally didn't push them on this or try to uncover their lies. Like I said, our culture has a severe problem with assuming experts are always honest and trustworthy. It's a totally flawed assumption and it resulted in hundreds of lives being destroyed in this case, but literally, nobody in the legal system including the defense really tried to probe whether the software really did work as the authors said it did. They just accepted the assurances made that it was perfect.