System unavailable: Various pLinux, xLinux, and Mac nodes cannot be reached

Nagios has identified the following machines that cannot be contacted, or whose jenkins agent cannot be reached.

Please let me know if there's anything I can do to help resolve these.

[Link](https://nagios.adoptopenjdk.net/nagios/cgi-bin/extinfo.cgi?type=2&host=build-marist-rhel79-s390x-1&service=Check+if+Jenkins+Agent+Connected)
(build-marist-rhel79-s390x-1) CRITICAL - Jenkins agent is fully disconnected

[Link](https://nagios.adoptopenjdk.net/nagios/cgi-bin/extinfo.cgi?type=2&host=docker-skytap-ubuntu2004-ppc64le-1&service=PING)
(docker-skytap-ubuntu2004-ppc64le-1) PING CRITICAL - Packet loss = 100%

[Link](https://nagios.adoptopenjdk.net/nagios/cgi-bin/extinfo.cgi?type=2&host=dockerhost-skytap-ubuntu2004-ppc64le-1&service=PING)
(dockerhost-skytap-ubuntu2004-ppc64le-1) PING CRITICAL - Packet loss = 100%

[Link](https://nagios.adoptopenjdk.net/nagios/cgi-bin/extinfo.cgi?type=2&host=test-skytap-ubuntu2404-ppc64le-1&service=Check+if+Jenkins+Agent+Connected)
(test-skytap-ubuntu2404-ppc64le-1) CRITICAL - Jenkins agent is fully disconnected

[Link](https://nagios.adoptopenjdk.net/nagios/cgi-bin/extinfo.cgi?type=2&host=test-skytap-ubuntu2404-ppc64le-1&service=PING)
(test-skytap-ubuntu2404-ppc64le-1) PING CRITICAL - Packet loss = 100%

[Link](https://nagios.adoptopenjdk.net/nagios/cgi-bin/extinfo.cgi?type=2&host=dockerhost-skytap-ubuntu2204-x64-1&service=PING)
(dockerhost-skytap-ubuntu2204-x64-1) PING CRITICAL - Packet loss = 100%

[Link](https://nagios.adoptopenjdk.net/nagios/cgi-bin/extinfo.cgi?type=2&host=test-macincloud-macos1201-x64-1&service=Check+Jenkins+Connection)
(test-macincloud-macos1201-x64-1) CRITICAL - Jenkins agent is fully disconnected

[Link](https://nagios.adoptopenjdk.net/nagios/cgi-bin/extinfo.cgi?type=2&host=test-macincloud-macos1201-x64-2&service=Check+Jenkins+Connection)
(test-macincloud-macos1201-x64-2) CRITICAL - Jenkins agent is fully disconnected

Start with the Nagios links and inspect the listed hosts: build-marist-rhel79-s390x-1, the Skytap Ubuntu nodes, and the MacInCloud macOS nodes. Check the reported network reachability and Jenkins agent connection failures; done means the affected hosts respond and their Jenkins agents are connected.

Written by the indexing model from the issue text.