net.ipv4.ip_forward not peristent, even in /etc/sysctl.conf

Currently i'm setting up a new Debian 11 Bullseye machine to act as a Wireguard gateway. Everything as usual, and simple. Unfortunately i am having a heavy issue regarding the IPV4 packet forwarding. It's a well known fact, that i have to uncomment #net.ipv4.ip_forward in the /etc/sysctl.conf file, to enable packet forwarding. Unfortunately,even when it's uncommented, the setting is not being applied automatically after reboot. I have to manually process the sysctl file using "sysctl -p" every time after reboot. What's wrong here? There is also no further sysctl.conf in sysctl.conf.d which may override this setting. I have also tried on a fresh Debian 11 system, with the same issue. root@wireguard:~# /sbin/sysctl --system * Applying /etc/sysctl.d/1-sysctl.conf ... net.ipv4.ip_forward = 1 net.ipv6.conf.all.forwarding = 1 * Applying /usr/lib/sysctl.d/50-pid-max.conf ... kernel.pid_max = 4194304 * Applying /usr/lib/sysctl.d/protect-links.conf ... fs.protected_fifos = 1 fs.protected_hardlinks = 1 fs.protected_regular = 2 fs.protected_symlinks = 1 * Applying /etc/sysctl.conf ... net.ipv4.ip_forward = 1 net.ipv6.conf.all.forwarding = 1 After reboot: root@wireguard:~# cat /proc/sys/net/ipv4/ip_forward 0 root@wireguard:~# cat /proc/sys/net/ipv6/conf/all/forwarding 1 I hope someone can help me, it looks like, it's being partially applied only, i don't know if it has something to do with the IPv6 setting. Everything apart from the sysctl.conf and the Wireguard install is set to default.