It sounds unusual for a house of that age to suddenly develop cracks.
New enough to have substantial foundations, old enough to have done any
settling.

Most importantly, has the movment stopped? Are you/the engineer
accurately monitoring the width of the crack from month to month? Did
the engineer suggest the likelihood of further movement?

You may need to pay for the services of a local engineer with
particular expertise in this sort of thing, rather than the insurance
company's.