I haven't actually bought a complex ticket on DL.com in a very long time, despite having tried quite a bit.

I can almost never find the exact flight combinations I want directly from DL and use Orbitz for most of my purchases.

The explanations of what's happening in the background sound good, but whatever the reason, I've never had them come back and say that they couldn't book it.

Often takes much less than 24hours too.