Occasional failure of X to start

[Richmond <richmond@criptext.com>]

I have a laptop with an nvidia graphics card, and a TV connected to the
TV out (svideo) socket. Sometimes X fails to start. All I can see in the
journal is:

Nov 07 19:38:37 systemd[1]: xdm.service: Main process exited,
code=killed, status=12/USR2 Nov 07 19:38:37 systemd[1]: xdm.service:
Failed with result 'signal'.

Where should I look for a more detailed error?

If I log in on the console and use startx then X starts.

i nvidia-legacy-340xx-driver - NVIDIA metapackage (340xx legacy version)

Linux 4.19.0-18-amd64 #1 SMP Debian 4.19.208-1 (2021-09-29) x86_64
GNU/Linux

I am using Debian 10 because this driver doesn't like kernel 5.

I am using xdm probably because I had much trouble getting things to
work with the additional monitor, so although I installed KDE I am now
using icewm with xdm.