I think this is actually a BUG, as this happens to me as well however, not when my monitor falls asleep (haven't tried it) but when the Simplify3D screen is not visible on the screen. For example, right now as I am typing this I am printing something on my makerbot replicator 1 (Yosemite) and the picture is how I have to have my screen setup at all times on the side or the printer intermittently pauses and sometimes causes that plastic buildup killing the print. I had emailed support and asked them if they could replicate the problem on their end, but they said they could not, not sure if they actually did it, so I don't think this will get fixed anytime soon until enough people make a fuss about it.
