Tested without any other mods that affects players. I also noticed this is more likely to happen to face baubles.

I don't think it'll be jarring actually, maybe a config list for baubles ids that would have disabled rendering while swimming? It could help for armor too in case there's any that don't render too well while swimming.

Could you let me know which mod you tested this with so I can reproduce it? I don't use too many Baubles mods myself so I'm having trouble thinking of one which adds a face bauble.

Here are the mods which added their own baubles renders that I used:

-Thaumcraft - Goggles of Revealing and Headband of Curiosity are affected. The goggles are shown in the picture above.

-Thaumic Periphery - This mod adds renders for the other Thaumcraft baubles which did not have them. I took a look and they weren't affected neither were the unique ones that it added but both of the pauldron baubles were affected.

-Thaumic Augmentation - Thaumostatic and Elytra Harnesses were not affected.

I also looked at these too:

-Thaumic Wonders - Night-Vision Goggles are affected. They're the same render as Goggles of Revealing.

-Botania - Any bauble that renders on the head are affected. Some of these would include most cosmetic baubles, The Spectator, Charm of the Diva, Engineer Goggles, Manaseer Monocle, Tiny Planet, and Benevolent Goddess' Charm.

-Artifacts - The Tiny Shirt, as well as any bauble applied to the arm such as the Pocket Piston, Fire Gauntlet, and Magma Stone. Head baubles are also affected like the Snorkel.

So far I've noticed that every one of the affected baubles are rendered on the head with the exception of the pauldrons from Thaumic Periphery and the glove/gauntlet/shirt baubles from Artifacts, both rendering on the arms. It also doesn't seem to matter which slot they use as long as they render on the head or on the arms.

Thanks for the additional info.

It looks like there is an underlying assumption that the player remains in a walking animation while these baubles render. I'm not 100% sure how to go about fixing this. Would disabling bauble rendering while swimming as a workaround be too visually jarring?