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Make sure that your simulation has been → cached before you trigger the render process. Without cache files a frame has to be simulated and perhaps even meshed before it can be rendered.
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- Add a compositing tag to an object and enable/define an object buffer.
- Open Render Settings (Ctrl/Cmd + B) > Multi-Pass.
- Right-click on Multi-Pass and select "Object Buffer".
- The "Group ID" has to match the "Buffer" value of the compositing tag.
For more information and a more elaborated workflow go to → "Multi-Pass Rendering".