A quite busy proxy server has lots of "SYNs to LISTEN sockets dropped".
I learned one cause could be a too small backlog size. But in that case the "times the listen queue of a socket overflowed" value should be equal (which it is not).
So what could be a cause for this behaviour? Maybe a broken nic?
We have 5 proxies, in 2 of which the two numbers are not equal, so this problem seems to be happening there.
Here the output from netstat:
$ netstat -s | grep -i list 238627 times the listen queue of a socket overflowed 8610307 SYNs to LISTEN sockets dropped
the servers have ipv4 and ipv6 traffic, maybe that helps?