Your new auditor is wrong. The problems with relying on a single trial court decision are that 1) the judge may have been wrong and 2) there is no publicly available record of the judge's analysis, the decision may have turned on a completely different issue.
As has been said repeatedly, the the term "official check" has no real meaning. If it is drawn on a bank and signed by a that bank's employee it's a cashiers check even if it says "Three Pound Pig" across the top of it.
From the Georgia version of the UCC:
(g) "Cashier's check" means a draft with respect to which the drawer and drawee are the same bank or branches of the same bank.
From the same source:
§ 11-3-411. Refusal to pay cashier's checks, teller's checks, and certified checks
(a) In this Code section, "obligated bank" means the acceptor of a certified check or the issuer of a cashier's check or teller's check bought from the issuer.
(b) If the obligated bank wrongfully (i) refuses to pay a cashier's check or certified check; (ii) stops payment of a teller's check; or (iii) refuses to pay a dishonored teller's check, the person asserting the right to enforce the check is entitled to compensation for expenses and loss of interest resulting from the nonpayment and may recover consequential damages if the obligated bank refuses to pay after receiving notice of particular circumstances giving rise to the damages.
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.