If the display is not connected directly but through an HDMI extender, scaler, matrix switcher, or similar AV device (e.g. Extron, Crestron), a modeline generated with {{ic|cvt}} or {{ic|gtf}} may be accepted by {{ic|xrandr}} (the output reports the new resolution as active) while the screen itself shows no picture. This happens because such devices are built around the fixed [https://en.wikipedia.org/wiki/CEA-861 CEA-861/CTA-861] timing table used by HDMI/TV equipment, and their receiver chips may refuse to sync to a VESA CVT-generated timing even at the identical resolution and refresh rate, since CVT and CEA-861 define different blanking intervals (and therefore a different pixel clock) for the same active resolution. This can happen even when the device's own EDID does not advertise the resolution at all: some devices' EDID under-reports what their receiver hardware can actually lock onto.
Compare the device's ow