Ok - this is very specific, but I’m looking for help. I have a 2011 Air with High Sierra. Working great as a web/MS 365 computer. Just set up 2 external monitors (1 via MDP and 1 USB). They both work when the clamshell is open, but when I close it, they immediately mirror each other. Also, the USB display has a lag with the mouse, but the MDP one doesn’t. I’m using a J5Create USB to HDMI cable.
Thoughts?
Thanks!
Arun
I’ve never used a USB to drive a monitor before, but I would suspect that it’s being transcoded somewhere at least once, and that is the cause of the lag. It’s probably unavoidable while sending over USB, but I will let others with experience comment on that.
EDIT: Does this provide any useful info? https://forums.macrumors.com/threads/resolved-external-monitors-and-mouse-lag.2194467/
Thanks! I did try to change out the cables to a better one, and it didn’t work. I also switched the monitors and got the same issue on the one connected to USB.
Do you know if I could get a MDP to 2 HDMI? Would it work to connect 2 monitors to that one port?
I have heard of MDP “hubs”. I think I read somewhere that one port could support up to 4 displays. I see this on Amazon, but I don’t know if it works to do what you need… seems promising though https://www.amazon.com/Startech-Com-DisplayPort-Multi-Monitor-Splitter/dp/B00XXPYOJW Oh Sh*t as soon as I finished posting, I read every line on that to see “NOTE: The product will not work with Mac” 
Time to see if anything else exists.
I’m out of my depth here, so I’m afraid I should stop commenting, but there’s this
Thanks so much for trying!!