What were you trying to do that didn't work?

Some post-installation scripts execute udevadm trigger internally (which lead to a "change" event).
This leads to removing PTP symlinks, e.g.:

# modprobe ptp_kvm
# ll /dev/ptp*
crw-------. 1 root root 249, 0 Sep 17 09:51 /dev/ptp0
lrwxrwxrwx. 1 root root      4 Sep 17 09:51 /dev/ptp_kvm -> ptp0
# udevadm trigger
# ll /dev/ptp*
crw-------. 1 root root 249, 0 Sep 17 09:51 /dev/ptp0

The PTP symlink is created only on ADD event, as per /lib/udev/rules.d/50-udev-default.rules rules:

 16 ACTION!="add", GOTO="default_end"

 84 SUBSYSTEM=="ptp", ATTR{clock_name}=="KVM virtual PTP", SYMLINK += "ptp_kvm"
 85 
 86 SUBSYSTEM=="ptp", ATTR{clock_name}=="hyperv", SYMLINK += "ptp_hyperv"
 87 
 88 LABEL="default_end"

What is unclear to me is why a CHANGE event deletes the symlink, it seems there is some reference tracking issue here.
Through enabling debug log level, we can indeed see that the symlink is detected as "not belonging" to the device anymore, somehow:

systemd-udevd[38299]: update old name, '/dev/ptp_kvm' no longer belonging to '/devices/virtual/ptp/ptp0'
systemd-udevd[38299]: no reference left, remove '/dev/ptp_kvm'
systemd-udevd[38299]: handling device node '/dev/ptp0', devnum=c249:0, mode=0600, uid=0, gid=0
systemd-udevd[38299]: preserve already existing symlink '/dev/char/249:0' to '../ptp0'

What is the impact of this issue to you?

PTP not functional anymore

Please provide the package NVR for which the bug is seen:

systemd-239-82.el8_10.1

How reproducible is this bug?:

Steps to reproduce

1.  Always

   # modprobe ptp_kvm
   # ll /dev/ptp*
   crw-------. 1 root root 249, 0 Sep 17 09:51 /dev/ptp0
   lrwxrwxrwx. 1 root root      4 Sep 17 09:51 /dev/ptp_kvm -> ptp0
   # udevadm trigger
   # ll /dev/ptp*
   crw-------. 1 root root 249, 0 Sep 17 09:51 /dev/ptp0
   

Expected results

Symlink persisting on CHANGE event.

Actual results

Symlink being removed.