It sounds like you haven't taken the time to properly define your device and monitor stanzas in your xorg config. Without which X may somtimes be switching which monitor is which when it autoconfigs.

See:
https://wiki.archlinux.org/index.php/Multihead

With attention to the configuring xorg section.

freemor wrote:

It sounds like you haven't taken the time to properly define your device and monitor stanzas in your xorg config. Without which X may somtimes be switching which monitor is which when it autoconfigs.

See:
https://wiki.archlinux.org/index.php/Multihead

With attention to the configuring xorg section.

I do not understand what you are thinkng, but after excluding compton from autoload, everything work correctly.

I was thinking that there was a race condition happening when X11 was
auto-configuring that was causing it to sometimes enumerate the monitors in
different order.

If such was the case writing proper (aka maunal) Device and Monitor Stanzas in
your xorg config files would create a fixed mapping as to which device is which
and also which is the primary.

Seems you found the issue tho so unless there is some objection I'll close this
as not-a-bug

XFCE has multiple issues piling up recently - we should probably
collect them into an epic and try to at least confirm them