Win10 on new laptop has several strange behaviors

Sorry, double post. Can't figure out how to delete it.

Just came back into the office, and I discovered the laptop had "lost" the external monitor. No display on the external, all windows moved over to the laptop display. (Which is probably the cause of some of the window resizing I've been seeing.) I've unplugged/replugged the HDMI connection on both ends, swapped in a new HDMI cable, power-cycled the monitor, removed both display adapters and rescanned, rebooted the laptop, tried Safe Mode, no joy. It seems I no longer have an external monitor.

garyfritz: I'd ignore most of this advice.
You bought a product and it's defective. It's not up to you to fix it.
Rather, it's up to you to return it for a refund or a replacement.

I've already contacted the seller to see what my options are. But it's a refurb so no doubt I'll have some challenges. Their first response was to do a full factory reset. I said "So that will put it right back into the state it was when you sent it to me, right? Most of these problems started basically immediately."