If x11-misc/autorandr-1.14 is installed, the udev rule refers to systemd service instead of autorandr call. cat /lib/udev/rules.d/40-monitor-hotplug.rules ACTION=="change", SUBSYSTEM=="drm", RUN+="/bin/systemctl start --no-block autorandr.service" Therefore autorandr is broken for openrc users in this version. It seems the same issue is back like the second one in https://bugs.gentoo.org/803545.
The issue is still not solved in x11-misc/autorandr-1.15 I thing the cause of comeback the issue is this change: https://github.com/phillipberndt/autorandr/pull/345 that was merged into 1.14