So your bank feels the appraiser and seller conspired to come in below the sales price. That doesn't make sense.
Your lender should know what options remain including a "reconsideration of value". My suggestion is to leave this in your Realtor and lenders hands
Well, not really that so much... more involved. But yes lender and agents are figuring it out. I’m simply educating myself in the ways of appraisals so I can know what I’m dealing with.