So it looks like the entire race vanished from my watch. I've been using the watch for a couple years now (though replaced twice under warranty) and use it daily for commuting. I have uploaded multisport events before, even recently. I am pretty sure it isn't user error, I use the watch nearly daily, roughly 20+ hours of biking and running a week.
I tried to upload with my wife's Surface Pro (which I have done so before with success) when I went to bed, and noticed it wasn't uploaded in the morning. I had the watch plugged in, it didn't die. I tried again and it didn't work. I looked at the history on the watch, and I don't see my race at all in the history! Yes, I did hold reset to save after the race. All the activities in the history now say they occured on Sunday, even if they were earlier in the week. It shows 63% memory remaining, so I know it isn't full. I know it was recording, I checked it through all the events (two lap swim course, so I looked at it on the turn around). It recorded the whole event.
I tried creating a short 10 second activity, it uploaded fine and shows the correct date and time.
Now the only issue I can semi think of is I was racing close to a time zone, my phone last year had a tough time deciding what time zone I was in so I manually locked it in to the correct one. But my watch worked fine at the same place last year, so I don't see why that would be an issue.
What else can I try?