Very, very strange behavior from the bank. They know that the processing of the [Grunderwerbsteuerbescheides] takes a long time in this region, they could certainly find this out without any problems. They also know that the [Grunderwerbsteuer] can be paid by you, they could at least take the necessary equity capital for this (you wanted to pay the incidental costs from equity), separate it, and use it to pay the [Grunderwerbsteuer]. They will also be able to find out that all other documents required for the execution of the contract are present at the notary.
I cannot see any reason why the bank is "burying its head in the sand" here and flatly refusing. The loan officer, with all due respect, has no idea. I would start here and assign his superior to solve this deadlock. It cannot and must not be that this financing is handled so poorly for you because of the bank's incompetence that you cannot fulfill your contractual (and by the way known to the bank) obligations.
Really unbelievable.