on Artifactory Powerpack 3.1.0, I see lots of messages of the form
"Sending HTTP error code 409: Old metadata notation is not supported
anymore" in artifactory.log. They repeat whenever replication of a
particular repository is running.
Re: Old metadata notation is not supported anymore
The metadata structure has been changed in Artifactory version 3.x and does not support the old metadata format that is used in version 2.6.5, so your target repository running on Artifactory 3.1.0 denies it with this error code.
What you can do is first upgrade the source instance to 2.6.7 and run the replication again.