when you can, run these and post the output. i would like to decode the EDID and see if it is correct. If you could swap sierra and high sierra to gather results it would be even better.
ioreg -l -x -w0 | grep DisplayProductID
ioreg -l -x -w0 | grep DisplayVendorID
ioreg -l -x -w0 | grep IODisplayPrefsKey
ioreg -lw0 | grep IODisplayEDID