Been happening a lot lately. On any trip this year I can no longer pull up the reservation after I've checked in for the outbound. The link in my profile won't work nor will a manual search regardless of the departure date I enter.
I'll get an email reminder to web check-in for the return with a link which does work successfully (haven't paid attention to what exact URL it's hitting). If I go to find the reservation myself (manually searching or using the link in my profile) I get that ugly error.
Really annoying.