OSD numbers flash and disappear when applying power

Hi everybody!

I got a strange problem.

In short, I have FC and ESC stack, when I apply throttle, from about 20 A, the OSD numbers start flashing and disappear, but the video from camera remains pretty good

Long story:
I have a QUAD VTOL which has two FCs, one F405 WING, the other F405, both speedybees, and the copter FC is connected to two 4x1 ESCs, so that one ESC runs the two front motors, the other ESC runs the two rear motors.

The camera signal is fed to both FC, and the path to the Copter FC is pretty long, about 50 cm.

The signals from both FC then return to video switch, so that I can select to display the overlayed OSD information from either FC.

The return signal from copter FC is about 30 cm to video switch.

As I said, when I start hovering, the OSD flashes and numbers disappear almost completely, but the camera video remains stable, if I switch to the Wing FC OSD, the OSD image remains stable. If it were a simple interference issue due to high current, I would expect the camera video signal to be also affected, but it only affects the white text of the OSD. So I am lost here. I do not know if I may have problems with ground cables, and change of .ground potential, but again, I would expect that it would affect the whole signal, not just the white text.

The ESC currents are high, from 50 A all the way up to 100 A, the problem begins with about 20…30 A, and I am running 4S.

Before, I have tested the Copter FC as independent unit in hover with the same current/voltage, without Plane FC and the display was working flawlessly, but the leads from camera to FC and from FC to VTX were short.

I am not sure if instad fighting th long cables, it is easier to setup MINIMOSD? I believe it is quite obosolete, but not sure if it can solve the problem of long video cables?