I have ZR2440w LCD monitor. When I have a GSM handy (Lumia 730) about 40cm or closer to the LCD (mostly from the left side), in case that the handy is receiving call or SMS, the LCD monitor backlight switch of. It takes about 5s after it gets back. The GSM handy could be left unconnected or in case of having it connected to a USB hub connection on the side, the problem is much worse.
I suppose that the EMC immunity of the monitor is not well done and the problem is quite annoying.