In those cases, whenever you open the Sequence asset, and the timeline (or the “frameline” which is on the right side of the editor), is already zoomed to be like 1-2 cm for each 0.001 frames, it may become “laggy” (very low FPS, and quite high CPU usage), probably in that case editor loads the whole shot at that high level of zooming, which is a huge amount of screens of the timeline to render for the editor.
Probably that is what caused high CPU usage and eventually crashed the UE4.
Speaking on how-to open that Shot-asset with super high level of zoom, im not sure. Maybe i have reopened the project after it was saved with that high level of zooming (reopened same Shot-asset). Maybe some other way.
Anyway if anyone else noticed this, you can comment on your own steps for reproducing.