Decklink signal -> DVI Projector

Dead guys,
I hope you have an Idea where this problem could come from.
We are feeding our projector through an internal Blackmagic Decklink Card via SDI to another Decklink Card, which converts the SDI signal to DVI.
So now the problem:
Our Projector needed to be fixed because a broadband cable was broken.
And now since we got the projector back it can’t handle a signal bigger than 1080, when sent via the Decklink cards.
But, what I can’t explain is that the projector has no problem showing the full 2560x1600 pixel resolution coming from a PCs internal graphics card.
I hope you have an Idea how this can happen?
I guess there is something wrong with the repaired projector..?

Thanks a lot and kind regards.

You can't sent non-standard broadcast frame sizes over SDI with BM devices. 2560x1600 is definitely one of them.
Afer HD/2K your next supported frame size over SDI is UHD (3840x2160).