Dell XPS13-9350 external monitor not working when plugged in via USB-C

Dear all,

Wonder if you can help me solve a problem. I have just received an XPS13-9350 from the Outlet last week. It was certified refurbished.

I've tried to connect a VGA monitor to it via a USB-C to HDMI, then HDMI to VGA cable. The HDMI to VGA cable works perfectly on my Inspiron 15. The setup also works if I full power down the XPS13, attach USB-C to HDMI to VGA to monitor, and then boot up. The external monitor then works almost perfectly (with the exception of Netflix's video player which makes it flicker blue - Youtube and local video are completely fine).

What I cannot do is plug in this monitor whilst the XPS13 is on already - which is inconvenient as I move on and off desk a lot, and powering down the computer every time is unhelpful. Oddly, the monitor will also not be recognised if I simply Restart from Windows. I have to fully power down and plug everything in before switching the computer on again.

I have updated BIOS, video card and Thunderbolt drivers since and none of these has solved the problem. My system info is:

DELL XPS13-9350

Windows 10

Core i7-6560U, Intel Iris 540 graphics

8GB RAM, 256GB SSD.