UI and Render Threads Not in Sync in CC2015+

My plugin is a modular effect, similar to Plexus, in that there is a main render effect, and a number of UI-only effects that provide data to the render effect (I've posted about this on a number of other occasions!).

When you apply the Renderer effect from the effects and presets panel, it uses Sequence Setup to automatically add the default data effects, so you end up with:

Module Selector (added automatically)

Builder (data effect - added automatically)

Instancer (data effect - added automatically)

Renderer (render effect - added manually)

This all works perfectly in AE pre CC2015, but in CC2015+ I get a bunch of After Effects error: internal verification failure, sorry! {invalid index in indexed group} errors, and the effect fails to render.

The reason for this seems to be that the UI and render copies of the project are not in sync. Indeed when I debug Smart Render, when it loops through the layer effects to gather the data it only finds the render effect, and none of the data effects. With no data, it renders nothing.

Now, if I save the project, close it and reopen it, everything works as expected, so the problem is limited to first applying the effect.

Any thoughts on how I can sync up the two threads?

Thanks, Christian