I’ve struggled with this as well, trying on 5.5.0 and 5.5.1 - using editor, rendering, adjusting sequencer, all giving the same crash results.
This may not work for everyone, but disabling SM6 Shaders in the Project Settings seems to have stabilized my workflow for the time being.
While some shader features seem to have been lost, fixing those shaders when I get round to rendering the final animation can be a “Future Jake” problem… 
But for now, while doing Previs and rough cuts of my animation, I can edit an animate my metahumans without the fear of me breathing in the wrong direction and causing UE to combust.
Hope this helps at least one other person!