TODO
SSH to your UDM
ssh root@<udm ip address>
<enter the password you set when prompted>
Configure the IPv6 Tunnel - You get the addresses from the Tunnel Details page on TunnelBroker
ip tunnel add he-ipv6 mode sit remote <server ipv4 address> local <client ipv4 address> ttl 255
ip link set he-ipv6 up
ip addr add <client ipv6 address> dev he-ipv6
ip route add ::/0 dev he-ipv6
ip -f inet6 addr
Test Connectivity from UDM
ping 2600::
Setup Address Allocation
TODO
You doing any load balancing?
To narrow things down I'd start with the ping packet loss... are you perhaps having an issue with connectivity to tunnelbroker?
ipv6 aside for now, do you have any packet loss on ipv4?
Try PacketLossTest.com - I usually run the "1080P Game Stream" approximation to really exercise things.
You could also test and look for [ipv4] packet loss between your router and the HE
<server ipv4 address>
in your config.