Packer v1.8.5 takes almost three times the build time compared to v1.8.0

I’m looking to update the packer version we use to build images from v1.8.0 to v1.8.5.
However, the build takes almost three times as long using the amazon ebs builder. It is using the same base AMI and provisioners, the only difference is the packer build version. Other builders (e.g. openstack) take the same approximate time to build the image.

For example,
using v1.8.0 (so amazon plugin v1.0.8): Build 'amazon-ebs.aws_instance' finished after 10 minutes 37 seconds.
using v1.8.5 (using amazon plugin v1.1.6): Build 'amazon-ebs.aws_instance' finished after 28 minutes 55 seconds.

We use ansible to provision the image, and we’ve turned on the ansible.posix.profile_tasks callback to see where the time is spent.

For v1.8.0, almost all tasks took less than 1 second, often fractions of a second.
For v1.8.5, most tasks take at least 1 second, often more than 1 second.
So the increase in time is spread across the ansible provisioner tasks.

Any hints as to why the build takes so much more time?
Were there changes to the SSH communicator in packer or the amazon plugin that could cause this?