I conjecture that the case finally reached a human being, whether due to my efforts, someone else's efforts, or random chance. The response is still a form letter, given the reference to other titles that do not comply with the KDP content guidelines. The previous messages never claimed that any of my titles did not comply with their guidelines.
They have not told me whether they are paying me the royalties accumulated between the last payment and the termination of the account, which their previous messages said would not be paid — my guess is not.
I am mostly through the process of putting Legal Systems Very Different from Ours up on Barnes and Noble and plan to complete it and see if I can, as I think is the case, publish with B&N and have the book on Amazon as well. I expect I will put the rest of my books back up with KDP.
My kindles appear to be back up on Amazon. It looks as though I have to republish the paperbacks but the information is still there, so it's just a matter of clicking through the pages. I am doing it for Machinery, will see if that works.