If the lists of items are completely different, you could try using the Multi-State Box to do the switching in your video. That way there would be no delay between them.
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Velo: Setting Up Your Multi-State Box | Help Center | Wix.com
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Example/Tutorial - Velo Tutorial: Working with Multi-State Boxes and Code | Help Center | Wix.com
As to why that would be happening, I’d check if you see it happening on the live website as well.