I am occuring a crash when trying to import binary exported file. I have latest version of spine editor and latest version of a plugin from git repository. Reproducing it with attached SpineUE4 uproject. Files exported with older editor's version do not cause a crash, there's just a prompt that they were created with older version. Anyway in this case spine data assets are empty.
Json animations seems to work well.
I'm not sure if its a proper solution but i found that you are checking in one place before calling updateRegion function if _region isn't null. After i added this condition to
if (sequence == NULL && region->_region != NULL) region->updateRegion();seems to fix this problem and assets are added properly to the project.