Blackmagic DeckLink Duo 2 and 1080P

Okey, I have another tricky question for you!

I've been using a Blackmagic Duo 2 for a few years.
I usually connect it via SDI cable to the cameras that output in 1080p50.
Now I bought some Hollyland 400s PRO for when I will use a gimbal or for when there will be small streaming and it will be difficult to use a cable.
Cable Duo 2 runs smoothly at 1080p50 (with SDI cable or HDMI to SDI converter).
The cameras/mirrorless come out in 1080p50, cable works perfectly.

When I attach the cameras/mirrorless with Hollyland to the monitor and I setting everything to 1080p50 the signal is seen perfectly but if but if I attach the Blackmagic Duo 2 (1080P50) I see no signal.
I only see the signal if I set 1080i50.
Via cable (sdi or hdmi converted to sdi) I see everything perfectly in 1080p50.

During these tests the cameras are the same, same setup. The cables used (HDMI and SDI) are always the same so I would rule out a cable problem.

What could be the problem? Why via Hollyland can't I get the Duo 2 card to work in 1080P50 but only in 1080i50?

That is because Dekclink Duo 2 is expecting SDI 3G level B for 1080p, whereas your Hollyland is outputting Level A. The workaround is to output HDMI from your Hollyland receiver and the use a mini converter to convert to SDI. All blackmagic converter output 3G SDI level B (switchable to level A as well)

I think a driver included a firmware update at some point that implements Level A input/output, if the system is running an old version of Desktop Video an update may fix it.