This looks like the same problem as reported here. I think it could be related to specific graphics drivers because reports are only recent.
I have updated the Demo programs :
Demo sender v2.049
Demo Receiver v2.049
SpoutSettings v1.049
Please try these to find whether the problem remains.
NestDrop uses DirectX9 internally but it’s compatible with all Spout applications that use DirectX 11.
The “secondary” adapter listed is the first one found. The UHD card is there but not listed in this diagnostic. The important one is the “display”.
Try the updated programs first so that we know where to look further.