X server not starting automatically

In my NomadBSD installation the X server is not starting automatically. Strangely enough, it began doing that only recently, it was working before.

After boot, it stays in text mode and asks for username and password. I log in with username nomad, then type startx from the shell, and everything works as expected. How to make the process automatic (again)?

Usually the command lines for starting x are in the file /home/nomad/.xinitrc
You can try sudo nano /home/nomad/.xinitrc

the default line are this:
export EDITOR=ee

. ~/.xprofile

[ -z "$1" -o "$1" = "default" ] && exec ck-launch-session openbox-session
exec ck-launch-session "$1"

So is it the same in your .xinitrc file ?

The file .xinitrc is correct. I checked again and noticed that the X server starts, but then stops with the following error

amdgpu: os_same_file_description couldn't determine if two DRM fds reference the same file description.
if they do, bad things may happen!

After that happens, I can login in text mode, and the X server starts if I type startx manually, which makes the thing even stranger.