Here’s a few more facts that may or may not be relevant.
I’ve been using WebCoRE presence sensors since you were required to install them in a separate instance. I have never migrated my sensors to my primary instance so I do have two instances of WebCoRE running. If I try to login to the dashboard for the instance that only has the presence sensors and no pistons in it, I also get the same error behavior, the log show a slightly different error (but it appears to be related to me).
10:27:26 PM: error java.lang.NullPointerException: Cannot invoke method leftShift() on null object @line 1712 (listAvailableDevices)
And there are two instances of the “WebCoRE Presence” in Live Logging. One simply shows a debug log for “Loaded 5 devices” (those are my presence sensors). The other shows “loaded 5 devices” and the error stated above.
For my main WebCoRE instance, there is only one WebCoRE showing in live logging and it shows only this:
92f5df3f-160e-4f68-a76d-663c2ef7b751 10:26:26 PM: debug getChildDevices(false), children=0
92f5df3f-160e-4f68-a76d-663c2ef7b751 10:23:46 PM: error java.lang.reflect.UndeclaredThrowableException @line 1699 (listAvailableDevices)