To be certain, if you're in the trenches of this anomaly investigation you'll get the full root cause and corrective action presentation, but that's not what this post is for.

You're correct on 1, we ended up hitting an edge case in their spec that they hadn't adequately tested to and the upper level management and engineering leadership were swift to accept the fault and implement fixes with us going forward.

From a SE perspective, as a "COTS" product, we had spec'd correctly to them, they accepted our requirements and then executed each unit's acceptance test plan (aka lower level than first unit quals or life tests where this should have been caught) on the ground without anything amiss. We ran through our nominal and off nominal cases at the higher level of assembly, but not for a duration that caught this on the ground. It wasn't until we were at extended operation on orbit the issues began.

Sadly like you state, space isn't like on the ground, you can't buy spares or replace things that fault, even for a true high volume COTS product that might slip through the acceptance testing.