House purchase is upcoming, EURIBOR surprise?

That somehow doesn't fit, does it?

With special repayments, you usually specify the maximum special repayment per year, for example 5%.

Does your loan have a maximum special repayment of 5% over the entire contract term?
€1100 p.a. is less than 0.5%

That's just a drop in the ocean..

Maybe just thick fingers... or it meant 11k or 12k p.a.

Thick fingers... Sondertilgung are 5% p.a. / amounting to mind. 1100€ per payment. The bank appointment took place now, all open questions could be perfectly answered. The banker was very relaxed, open and explained everything understandably. The financing has not yet been finalized due to notarial issues, we were advised against finalizing the financing before the notarial purchase contract is predictably signed... The problem then was that the offer would no longer be valid.... At first, a big disappointment in our eyes! We then looked for cosmetic defects in the contracts, which fortunately we found. Subsequently, the offer "had to" be withdrawn and we were promptly given a new offer with better conditions - additionally, our fixed interest rate period and everything related to it is extended. Very cooperative and customer-oriented, that exceeded my expectations. My experiences with my main bank, where I have had my checking account since my youth, are catastrophic by contrast.