I had this exact same issues yesterday.
I used the cluster update tool to install this pre-6.7 update to both publisher and subscriber.
From release notes:
"Through the Cluster Upgrade Portal — If a 6.6.7 or 6.6.8 version is upgraded to 6.7.0 through the Cluster
Upgrade portal, a preparation patch is required first, and must be applied only to the publisher."
Guess that was my issue... RTFM. sigh