This reminds me of the thread I posted a while ago, asking if anyone else's professional printers act like a moron occasionally. I've had mine feed an entire 40' roll of canvas through while I wasn't near it. Luckily, the canvas rolled itself up, so it wasn't ruined. I've had mine autocut right through a print that it's just done. (
) I'd beat mine occasionally, but Epson support swears this won't get the printer back in line...
Anyways, not sure this is your issue, but I had a similar issue with my Epson 9900. Using the Epson driver, if the hard drive Windows is spooling on completely fills up, my system doesn't kick an error -- but prints up until where it's spooled. I only find out when I see an unfinished print.
I'm more familiar with Photoshop. It can grab a bunch of hard drive space for its scratch files, so I make sure there's always plenty of space available on my main drive. Not sure if LR does as much of this. You shouldn't (in my opinion) have to stop all work.