Xrandr and external monitor

[Fungal-net]

> I just discovered running xrandr --listmonitors that, while the internal laptop monitor is labeled eDP-1, xrandr identifies the external monitor as using DP-1 although it uses the laptop HDMI-connector. Further, while mate hardware display monitor also identifies it as using DP-1 - possibly based on xrandr output - the monitor itself tells me it is connected using its HDMI1 connector. xrandr does report the correct display resolution, though.

Are both ends of the cable hdmi, no adaptors?  Usually hdmi - hdmi or dp - dp seem pretty accurate, while when you go from one to the other they are a bit unreliable.  Is the monitor on before you boot, or are you connecting while the system has booted?

Pretty much all guis use xrandr output.  Since you are not listing the make and model of the monitor do a search and see if firmware are available specific to this monitor.  Also which kernel are you using (different versions tend to behave a little different).  
In most cases the chipset in the monitor provides the firmware needed to properly identify itself in the system, but I've seen many deviations.  Do you also have svga plugs on both?  

Last question, are gfx native intel/amd or is there something like nvidia involved?  It is not a good day to be mean to a stranger but tomorrow I may say "ask nvidia then "  :)