Network crashes NetBSD 10_RC6 (probably ISP issue)

########################
# part of /etc/rc.conf #
########################

ip6mode="host"
#ifconfig_wm0 static addresses for IPv4 and IPv6 are set in /etc/ifconfig.wm0
defaultroute="192.168.1.1"
defaultroute6="fe80::1%wm0"
...
npf=YES
npf_rules="/etc/npf.conf"

#############################
# part of /etc/ifconfig.wm0 #
#############################

inet 192.168.1.20 netmask 0xffffff00
inet6 2001:fb1:138:760f:2cc7:1066:153f:e957 prefixlen 64
up

############################
# part of my /etc/npf.conf #
############################

# /etc/npf.conf
$ext_if4 = inet4(wm0)
$ext_if6 = inet6(wm0)

$services = { ftp, ssh, http }

procedure "log" {
	log: npflog0
}

procedure "norm" {
	normalize: "random-id" #, "min-ttl" 512, "max-mss" 1432
}

group "external" on $ext_if4 {
	pass in final proto tcp to $ext_if4 port $services apply "log"
	pass in final proto tcp to $ext_if4 port 1024-65535	# Passive FTP
	pass in final proto udp to $ext_if4 port 33434-33600	# Traceroute
	pass final on $ext_if4 family inet4 proto icmp all # Ping
	pass stateful out final family inet4 proto tcp flags S/SA from $ext_if4 apply "norm"
	pass out final family inet4 proto tcp from $ext_if4 apply "norm"
	pass stateful out final family inet4 from $ext_if4 apply "norm"
}

group "external6" on $ext_if6 {
	pass in final proto tcp to $ext_if6 port $services apply "log"
	pass in final proto tcp to $ext_if6 port 1024-65535	# Passive FTP
	pass in final proto udp to $ext_if6 port 33434-33600	# Traceroute
	pass final on $ext_if6 family inet6 proto ipv6-icmp all # Ping
	pass stateful out final family inet6 proto tcp flags S/SA from $ext_if6 apply "norm"
	pass out final family inet6 proto tcp from $ext_if6 apply "norm"
	pass stateful out final family inet6 from $ext_if6 apply "norm"
}

group default {
	pass final on lo0 all
	block all apply "log"
}