Gaps under door! Uneven floor! Floor boards now coming loose.

I doubt the gaps are anything to do with expansion and contraction. It is more likely that there has been movement in the property over the years which is rarely anything to worry about. Foundations can not be inspected without excavating or at least lifting floor boards to inspect . I would call your insurance company again and say you are not happy with the surveyors report and ask them to put down in writing what he has said. It could be that you are not covered for this defect but its worth a try.