That's not a fault of the app, but a system issue (certain processes don't yell loud enough to keep the system awake). Try "CaffeinateMe" from the App store (I'm assuming here, next time begin with "Mac" or "Windows", and go from there.
Not saying that it's a "fault" of the app, but it would be nice to offer this option, no?
Edit: Found conflicting info on this one. Some claim that Lightroom should prevent the box going into sleep during certain processes like export. Perhaps it's a problem with InstantGo (aka Connected Standby)? https://blogs.windows.com/windowsexpe...