Sysctl kernel parameter cannot be reverted

I used to have net.ipv4.tcp_mtu_probing = 2 in /etc/sysctl.d/local.conf. However after I removed the line and rebooted, the value is still 2 (the default is 0). What is happening?

$ sysctl net.ipv4.tcp_mtu_probing
net.ipv4.tcp_mtu_probing = 2
$ systemd-analyze cat-config sysctl.d | grep tcp_mtu_probing
# Nothing

It may have been copied into the initramfs on a kernel update, in which case you can rebuild it with dracut -f.

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$ lsinitrd
-rw-r--r--   1 root     root          115 Nov 16 00:00 etc/sysctl.d/local.conf