OC MCP Displays goes OFF and ON while using EFIS

Hi all.
I hope I can discribe my problem for everyone to understand.

First I had a problem with the not well working QNH-Encoder on the OC EFIS. I opened it and found out that the cable coming from the encoder was crimped a bit between the metal cover of the EFIS and the board. I could fix this problem by changing the position of this cable. Put all together and the QNH-ENCODER works well now BUT...
When I now use the EFIS the displays of the MCP went OFF and ON for a second (not flickering)..not everytime but sometimes. When the display came back again they have kept the data.
Both have 5 V supply and are connected to the same USB-Hub (BELKIN with its own power supply).
I've checked the connection of the power supply to the MCP but it seem o.k.
I've read somewhere about shadowing...maybe this is it here too ? Don't know.
Maybe do you have an idea ?

Many thanks for help.
Greets, Kai