I'm running into something similar. Have a OW saver award booked for 07 June, 4 people, VIE-AMS-ORD-FSD. VIE-ORD is now showing availability for all 4 in saver. Tried to change itinerary online- got all the way through putting credit card info in and then received an error. Credit card charge showed up as pending.

Called United, got an incompetent agent who tried to just tack the VIE-ORD onto the existing reservation, so that it showed VIE-ORD multiple times plus the all the original segments. Told me everything was fine and call back within 24 hours to confirm. Yeah, right. I called back in 40 minutes.

Second agent transferred me to "international desk" and third agent managed to change itinerary back to the original but couldn't replace the first 2 segments with the direct flight. She put me on hold and talked to someone else and said try again tomorrow.

Next day- still see the saver award for VIE-ORD on UA site and on partner sites. Called United, agent tries again to change and says she can't because of married segment rules and because this a voluntary change. I mentioned that the ORD-FSD flight number had changed from the original booking...would that be case enough to change to "involuntary" change? Nope.

So I guess I'm watching for both VIE-ORD and ORD-FSD to show up in saver or for a significant schedule change. Perhaps I should have left it the mess that the first agent left- there was obviously no way that could have been a valid itinerary and maybe they would have had to open up saver space again on the ORD-FSD segment.