X_SYNC_UNCONFIGURED
Means
a live hook needed the page socket and no sync target was configured
Typical cause
a live useQuery (or anything else that needs the page's one socket) ran, and neither installRealtime({ sync }) nor the document's <meta name="ultimate-sync"> named a target. x dev and the container render that meta on every document; a page served some other way does not
Fix
serve the page through x dev or the container, which render <meta name="ultimate-sync"> (and SYNC_URL where the socket is not on the page origin). Or pass installRealtime({ signal: createSignal, sync: { url, buildId } }) from @ultimat3/realtime