After a lot of pain trying to work out IPv6 problems ahead of rollout, I discovered that this is a problem that's been known by Kaspersky for many years.
In short, from other threads, it's that something is adding a hop by hop option to the packets, which ends up with the packets being dropped by router.
We're running version 18.104.22.168 on 30 workstations, which are up for renewal at the end of the year.
In some other threads, there's been claims that it only affects Windows 8, but i can confirm that it most definitely affects Windows 10 1809 as well.
Why is it still a problem?
Will it be fixed?
When will it be fixed?
I couldn't find any setting to turn this behavior off, but maybe there is one?