This is a very large gap, but as someone who has recently had four appraisals done in the space of 6 months (long story), I have had a swing of 40% from the hig

This is a very large gap, but as someone who has recently had four appraisals done in the space of 6 months (long story), I have had a swing of 40% from the highest to the lowest (in all cases house was unchanged, and appraiser saw me in person each time). Appraisal is very difficult to do well, and different appraisers have different ideas about market trends (part of the reason for my wildly differing appraisals were different expectations for property appreciation in the neighborhood).