Dear Georg,
replying on my iPad, so need to make this short.
I have the same setup (less the ICP), and the same issue since the latest update. L/R MFDs flicker a bit and are dimmer as displayed. The center display (EHSI) compass I was able to fix last night temporarily. You need to program the brightness detent button, then use that in conjunction with the CRS switch. Once completed, hold the detent button and CSR switch L/R, the display will brighten up or lower to your desire.
Still need a fix on the 2 other displays.
Hope this helps.
Braz90