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If the scene contains fluid and mesh nodes both elements will be cached together when you hit "Cache Simulation". You can avoid this if you make the "Mesher" node inactive (disable the green check mark in the Cinema 4D's "Objects" manager).
Change the "Cache Folder (macOS | Windows)" to your own needs before you cache the simulation.
Visual Hint
When RealFlow | Cinema 4D is in cache mode ("Use Cache" is enabled) you will see a hint in the HUD and that the main logo in the viewport has changed:
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