Right after the Clarity effect ends, the underwater view becomes 100% clear for a moment before returning to normal. It looks like a brief blink.

Mod loader: Fabric
Mod version: [1.20.1] Hybrid Aquatic 1.4.2

The effect is present but ends soon.

The blink happens right when the effect must end.

The effect has ended.

Thank you for your report!
We know about this bug, it's existed for a while, but we think it's harmless and so it's not a priority for us. Nevertheless, we'll take a look at it and see if we can fix it in the coming patches

Unfortunately I think this is just something with how Minecraft renders fog, so Im closing this issue and might come back to it at a later date