Jenkins version: 2.156
(Working) SSH Slaves plugin version: 1.28.1
SSH Credentials plugin version: 1.14
Credentials plugin version: 2.1.18
Jenkins is running on an ArchLinux box in my office. The build agents are two Mac Mini machines running High Sierra, also in the office.
After updating the SSH Slaves plugin to 1.29.4 and restarting Jenkins, both my build agents are listed as offline, and there's 1 problem indicated in the Jenkins header bar. It's the "data stored in an older format and/or unreadable data" message.
Clicking Manage there takes me to the Manage Old Data page, where the only thing listed is the exception mentioned earlier, in the Unreadable Data section:
The only alert on the Manage Jenkins page is a yellow banner saying that data is stored in an old or unreadable format.
There are no errors in the Jenkins System log page.
Clicking into one of the build agents says "This agent is offline because Jenkins failed to launch the agent process on it."
Looking at the build agent log, all it says is:
[12/29/18 14:19:55] [SSH] Opening SSH connection to XX.XX.XX.XX:22.
[12/29/18 14:19:55] [SSH] SSH host key matches key seen previously for this host. Connection will be allowed.
[12/29/18 14:19:55] [SSH] Authentication failed.
[12/29/18 14:19:55] Launch failed - cleaning up connection
[12/29/18 14:19:55] [SSH] Connection closed.