Same here, did some testing and .las/.laz files are broken on my end.
Upgrading 5.5 project with previously imported point clouds to 5.6 → crash.
Trying to import .las/.laz files on fresh 5.6 project → unknown file type “las”.
Chatter on other forums mention same issue for many users.
I have submitted a bug report by following @SupportiveEntity 's link and hope dearly Epic will look into this for 5.6.1