I wouldn't worry about it.

An oft-reported problem with United's systems is that partner flights drop off before they're flown. What you're reporting is the opposite. It's likely not even a problem, and if it is, it's far less catastrophic.

United has some serious interconnection issues with other carriers. I have a couple ressies now that were cancelled and refunded. Now all of a sudden, some partner segments have returned and are showing up.

I don't have time to chase down their technology problems. I call them if the error impacts me, and I ignore stuff like this.