All that was done was updating firmware on the S1300 to 3.203. Per the GUI, no settings were saved to “prevent compatibility issues.” When I pressed and held the Mesh button until the blink pattern changed, about 5 seconds, I saw the separate 5G SSID disappear and the mesh light blinked like it was attempting to set up mesh. When reconnected to the router, I was not able to return to the GUI while it was in Mesh mode. I was able to return to the GUI as soon as I shut off the Mesh mode without changing any other settings. This process was tried with multiple computers and different OS without changes. This resulted in our reverting back to firmware 3.105, but it is behaving the exact same.
So, that’s why I’m wondering if not maintaining settings and plugins may have caused the problem, hence the question regarding a lost plugin.