Did you ever get any answer to this?
I just recently tried enabling the ssh API and ran into exactly the same problem. Since I hadn't used this feature before, I had assumed it was related to my setup-- but your post makes me think there's just something broken in this recent build.
Ironically, I was setting this up as a counter to a push in our organization to move to a different password manager because PMP didn't allow for CLI access... I was trying to show that that wasn't the case, but if this feature isn't going to work reliably then we are going to have to switch.