My reservation also went nuts on UA.com: BKK-SYD and a later connecting flights went missing. UA has now booked me onto TG472 but with a minus (!!!) 1 hour 20 minute connection in BKK.
Apparently TG476 was causing all sorts of trouble for the UA supervisor and she could not grab a F seat (or any seat for that matter). She did say I was waitlisted for Business Class though (I was booked on a F award). UA was super apologetic, which was surprising, because it was not even their fault.
I have decided to sent TG an email too, fearing that UA's rebooking may have messed with TG's attempts to re-upgrade passengers.
Let's hope TG has a better attitude to maintenance and safety than route planning and IT.