BDU did have concernes but the backroom people told them that his was imposible and that enigma had been compromised was not even worth considering.
Donitz did take steps ....staff numbers were cut .everything was on a need to know basis but he was always told ....no your codes are 100% secure.
Some Commanders also had doubts.....these he too considered and was told the same thing.
On the other hand codes can only tell so much and he Allied hand kept their cards very close to their chest...covering the fact thattey were "reading over the shoulder of BDU" and at all levels of germany's command structures. Diect evidence that the Allies new would have been hard to estiblish.
HF/DF. may have covered up the actual reading of the codes to some extent, to us with hindsight and what is now known , when your best men are saying otherwise ?