Since I've added this for 3 weeks it's working fine, however OPT1 has failed just a few times during office hours. No complains about loss of internet or failed PAP2T device for now. I will stick with this workaround until better solution comes up.
In short:
Change /conf/config.xml
<system>...
....
<afterfilterchangeshellcmd>/usr/local/bin/reset_states.sh</afterfilterchangeshellcmd></system>
Create /usr/local/bin/reset_states.sh
#!/bin/sh
sleep 60
/sbin/pfctl -F state
sleep 40
/sbin/pfctl -F state
chmod 755 /usr/local/bin/reset_states.sh