Started looking for flights, this happened to be DFW-LHR, not that is causing the issue, but got:

Our system is having troublePlease try again or come back later.

Makes it really hard to plan and book flights.

At first I resubmitted several times getting this message.
Between looking for this thread to see if others were having issues today and then resubmitting the flights again, it started working.

This falls under the category of 'you've got just one thing to do', this type of thing should not happen for your core IT functionality. And I know my expectations are too high.