Lolz.
It's happened me loads of times.
I'd be working on an AUX channels, go do something - plug something in, chat, scratch etc. etc - come back to the desk and start to mix - nothing happening...
I've usually forgotten to turn back to the LR page. It's something I'd like changed in a future update, different coloured backgrounds on LR, Aux1 etc.
This may be what happened to you - it's happened to me plenty of times until I caught on.
Hope this helps:)