What version of InDesign? What operating system?
Yosemite 10.10.5 on MacBook Pro (Retina, 15-inch, Late 2013)
InDesign CC2017 (subscription updated)
Dropbox files are local, not server based, so I doubt it has anything to do with the network. Next time it crashes, please post the crash report on pastebin.com and provide a link to it here.
DO NOT POST CRASH REPORTS HERE