I finally have a working solution to this age old issue. I worked with Cohesive and they provided a solution that works really well. Setup instructions are in the Youtube below and key configuration settings are

dpdaction=clear

dpddelay=15s
dpdtimeout=60s
connection=receive
connection-rekey=no

You need to contact them for a special 2 x Remote Endpoint license which is different to the two options currently available as AMIs from AWS.

WHat is the 'SD-WAN featureset' and how do I get this?