I saw this today while testing.
mirthsync -s https://localhost:8443/api -u admin-p admin -i -t . push
WARN : An unexpected response was received from the server...
WARN : Status: 200, Phrase: OK, Body: {"boolean":false}
Failure(s) were encountered during the push
At the end the channels were there but they were not in the groups they were in before.
Using -f fixed it though (after delete all the channels).