I have a 13” MacBook Air (mid 2013) with OSX Yosemite and bought a BenQ SW271. It was all working nicely in 1440p through DisplayPort cable. After update to High Sierra it shows no signal detected but in MacOs i can see the monitor is connected and i can change the resolution etc.. I tried reinstall MacOs multiple times also from internet recovery(option+cmd+r), reset nvram, smc, changing resolution, plug unplug, turning it off for a day all kind of voodoo I found on YT but so far no luck. I called Apple but they didn’t have solution until now. Any idea what might be the problem?