RT-AC68U disable IPSEC NAT helper

[bits]

I have an Asus RT-AC68U running Rmerlin 384.19 and I find if I have multiple IPSEC tunnels connected to the same destination I get significant delays in outgoing packets.
These delay do not occur with other routers.

Many routers have an IPSEC passthrough setting that tries to manipulate IPSEC data on port 500 to try to overcome issues with NAT.
However Asus the "passthrough" setting is instead a firewall feature to simply allow or disallow connections on port 500.

Is there an IPSEC NAT helper enabled that may be causing issues?

 

[bits]

I just proved this exact same problem also occurs on DSL-AC68U running official 3.0.0.4.380 it shipped with and also latest 3.0.0.4.386_39648
Also still occurs with NAT acceleration disabled.

This problem appears to only affect Asus routers as I have tested with multiple other brand routers that do not have this issue.