For anyone struggling with models from 3DS Max: I managed to fix it by setting the system units to cm and using the Rescale World units Utility to set everything back to the correct size, then re-importing in unreal.
Beware that Max has both ‘Display Units’ and ‘System Units’. Just because the program shows you sizes in cm doesn’t mean they are actually in cm! (this took me way too long to figure out, you have to set both unit scales to cm or it won’t work properly).