You are out of disk space or memory on that primary member, or its hard drive has failed as Val said. Since the primary firewall is showing as disconnected, that means that the cpd daemon is dead or impaired, and the fact that sshd can't get any resources for your incoming connection confirms that process/user space has insufficient resources to do anything. However most traffic inspection operations take place in the kernel, which preallocates all its needed memory in RAM and has no dependence on the hard drive once successfully booted up. If the hard drive has indeed failed, be prepared for the primary to not boot back up when you power cycle it. Make sure your secondary member is ready to take over, and also anticipate that you'll need to do a restore on the primary after replacing the hard drive.
Gaia 4.18 (R82) Immersion Tips, Tricks, & Best Practices
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