KVM and Screen Resolution not working as designed

Hello,
we are using the following hardware to view our server (T430, R320, 3x R730). Dell KMM DKMMLED185-205 18,5-Zoll + Dell DMPU108e 8-Port Remote-KVM-Switch. Unfortunately is it not possible to set this kvm up to show a picture when connecting to the servers. One works, the other shows "no signal".

I tried to adjust the screen resolution in the kvm under default screen resolution to 1920*1080, 1440*900 and 1024*768. I have no idea to solve this issue. FW was updated to "Anwendung 2.4.0.25463 " "Boot 2.4.24247".