Ben,
Crashes are most often related to memory issues. And both working space (RAM) and disk writing and overhead issues (free hard drive space) are the primary factors that are usually in play.
(this presumes X loads up properly and works smoothly prior to the copy attempt.)
Make sure you have ample headroom on your drives (and possibly de-fragment them) so that X has a lot of clear headroom – and if you’re moving large projects, make sure you have enough RAM in your system so that X can use it for shuffling chunks of the existing projects off to the new locations.
There certainly might be other factors in play, but this is the first place I’d look if I was in your shoes.
Good luck.
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