If the internal PMS setting "Settings > Network > Secure Connections" is changed from the default setting of "Preferred" to "Required" the pod is forced to perform a restart.
When re-deploying the Plex pod, docker/k3s is trying to test all of the ports that have been forwarded to the pod. During this test the local console returns the following every 5-10 seconds:
IPVS: rr: UDP <PodIP>:32412 - no destination available IPVS: rr: UDP <PodIP>:32414 - no destination available
This leaves the WebUI to display "Deploying" for the status fo the pod, preventing >_Shell access, and preventing the rendering of the "Portal" button.
The pod has in fact deployed and is operational. If you navigate to the pod via https://<IPaddress>:32400 (instead of the TrueNAS default of http://) the Plex WebUI will display, and Plex is fully operational.