I've found that some of my larger pieces can't be resized to 720 dpi in Lightroom. The job seems to execute, but produces blank output.
I've seen this as well. If I try printing a large print from my IQ180 files or some of my stitched files at 720dpi from lightroom, I get a blank print. I have to go back down to 360.
Doesn't happen often since not many files printed very large have enough resolution to be higher than 360 which may benefit from using 720 in LR, but has happened a couple of times.