Proxy stops working after some time.

Hello, I am sorry for a bug report, as this is more of a question (by hopefully can be interpreted as a "usability issue" :( ).

I have an ISP box, and my own router, with two interfaces, following it. em1 is connected to the ISP box, the em2 is connected to the LAN. The router has ndppd running with the following configuration:

route-ttl 1
address-ttl 1
proxy em1 {   
   router yes
   timeout 5000   
   autowire yes
   keepalive yes
   retries 5
   promiscuous yes
   ttl 1
   rule my:ipv6:prefix::/64 {
      iface em2
      autovia yes
   }
}

Things work... "kinda". I mean, they work most of the time, but sometimes routing starts to fail for no obvious reason. It takes about half an hour, and then routing is back. Sometimes more, sometimes less.
There seems to be nothing in the log, so I hoped to ask for some help with debugging.

[valerius2k]

Hi, I also have something like this. I set up an ipv6 proxy by following this article: https://blog.vpsville.ru/blog/howto/133.html. The article describes setting up an ipv6 proxy with 3proxy and ndppd to serve a number of proxies with addresses from that /64 ipv6 range. The config is the following:

route-ttl 30000
proxy eth0 {
    router no
    timeout 500
    ttl 30000
    rule my:ipv6:range::/64 {
        static
    }
}

All settings are in the article above. The article is in russian, but all configuration settings
don't need translation. The article is a blog of one hoster which sells VPS'es with /64 ipv6 ranges,
and they published a tutorial of how to set up a multiproxy configuration.

But that hoster has some complaints to their support, because of ipv6 stopping working periodically.
The same I observe too. First, I thought that was a fault of that hoster, and tried to set up a proxy on
another hoster, having the same problems. Then I looked into this ticket and I can acknowledge having
similar issue. So, it just stops working periodically, then works again, without obvious symptoms. No
messages in logs.

Could I do some help with debugging?

[domosekai]

I have experienced very similar problem and made a patch. Try out to see if it works for you.
The problem that I found was when the session is in INVALID state it can't be put back.
domosekai@b366dd4