I think you're right that this is a mess, my only uncertainty is whether it's garden variety incompetence or active bad faith. For an auditor to fire you, either you have to not be paying your bills for a long time or you have to be deeply uncooperative or insanely demanding.

That said, the consensus I've heard from my audit colleagues (I work in public accounting) is that no one has the slightest freaking clue how to audit crypto. So I could see the audit taking exceptionally long, causing friction in the relationship which eventually blew up into a full on breakdown. If that's the case, Tether's leadership probably had a poor understanding of the complexities involved. Sometimes that's the client's fault, but sometimes it's the accounting firm making too aggressive of a pitch to sell the work.

But the bank account issue makes me think bad faith. That shows a willingness to disregard rules and mislead fiduciary business partners, which is pretty much an auditor's nightmare client.