This is a solution to a problem without knowing what the actual cause of the problem is.
LibreOffice 5.3.7.2 on MacOS High Sierra (10.13.2) kept crashing when I was trying to open certain files. Not every file would cause it to crash, but there were a few that did, both documents and spreadsheets. No idea why it was crashing, but trying to open those certain files caused LO to crash immediately.
On a whim, I tried to open the files from a new administrator username on my computer (not a different LO user, but a new computer user), and it fixed the problem! I could open all files with zero problems on the new computer user.
No idea why this happened, but figured I would report it in case anyone else is experiencing the same problem, hopefully this fixes the issue for you as well!