Cascaded setup - "recv(): No route to host, closing connection"

[salakis]

I have a rather bizarre, but in my case required setup with two instances of sniproxy running behind each other (basically: client[ipv4 only]<-->sniproxy1[dual-stack]<-->sniproxy2[ipv6 only]<-->target host).
So far this sort of works, but I often get an error message with "empty response" when pulling data through this cascaded sniproxy setup.

I switched the error logging to debug and it is filled with

2016-05-02 20:57:48 recv(): No route to host, closing connection

2016-05-02 20:58:33 recv(): No route to host, closing connection

2016-05-02 20:59:09 recv(): No route to host, closing connection

2016-05-02 20:59:09 recv(): No route to host, closing connection

The two servers are not on the same subnet and there is a latency of about 100ms between them.

Is there any way to get this fixed? Thanks!