I got issues like this as they wanted me to meet the covid doc rules for germany despite the fact i was transiting on the same ticket and they could see i was in germany for less than 24 hours.
So you may find this is becauae they think there is an issue wirh your covid docs.
In my case they wanted me to get a negatuve test, which i did rather than tey and aeguw it out at the airport when it would be too late if they still said no