Recently an udev rules was not executed. After some investigations, it was a symlink to a user file with these permissions :
-rw-r--r-- 1 user user
changing ownership to -rw-r--r-- 1 root root
and reloading indev rules with udevadm control --reload
solved the problem.
I understand that for security reasons it is better to have system files owned by root. Does that mean udev checks rules owners and rejects non-root rules? Is there another explanation?