This issue has been solved by using the 4.16 kernel (from debian-9 backports) and adding the following file (with contents):
cat /etc/modprobe.d/iptable_raw.conf options iptable_raw raw_before_defrag=1
This issue has been solved by using the 4.16 kernel (from debian-9 backports) and adding the following file (with contents):
cat /etc/modprobe.d/iptable_raw.conf options iptable_raw raw_before_defrag=1