Flying UA956 tomorrow with my girlfriend in BF on two different PNRs (as she's flying home after the vacation and I head on to TLV).

Up until about an hour ago we were on a pmUA 763. We got the check in text/email, girlfriend clicked it first, and noticed her seat had been moved to the other side of the plane. I clicked the link and saw they swapped aircrafts, and since we're traveling on different PNRs they clearly had no reason to keep us seated together.

No harm done, there were pairs of seats on the window available so we each grabbed a seat and seems like we've reseated ourselves together. Which gets me to my questions:

What are the chances of them changing back to the pmUA frame and us again being split up? Or someone who had been in GF complaining about a seat and one of us getting moved away from the other?

Part of my concern is that we weren't able to successfully check in online, we each got an email telling us we have to scan our passports at a kiosk before we can be checked in, so I'm concerned about someone moving us around again. We're planning on getting to the airport a little extra early tomorrow just to try and lock in two seats together, just curious about what the likelihood of things moving around again is.

And as an unrelated question, the general opinion seems to be that the pmCO seats are a little more private since you don't accidentally lock eyes with someone across the aisle, am I wrong to think of this as an upgrade?