It could be flaky soldering ( I've seen a few people have problems with pins on their Zero even with apparently great soldering that have been fixed with a touch up ) or it could be something else.
We'll do some investigation this end when we get some time, to see if there's any way to reduce the error rate. Otherwise we'll just squash it in code. It sounds bad, but in practice you can just fire out updates to the driver chip constantly and it's irrelevant if there are failures- as long as they're not consistent.