@mrkiouak Om next has a few optimisations to avoid re-rendering everything whenever something changes. When you call (om/set-state! this... you queue a re-render of just the component instance this. Om Next will then call ui->props on this, which will in turn parse the component's query (if it implements IQuery) and update its props. The error your seeing happens when Om Next is not able to find the query via the reconciler - which it doesn't need to do on the initial render.

This has caught people out before (e.g. https://github.com/omcljs/om/issues/791) and I suspect you might have hit the same query gotcha ("stealing" another component's query)