When an air hole is in water, the bottom of the water's texture is transparent until passing into the gap. The water brightness effect in Bedrock Minecraft makes it indistinguishable from the surrounding environment. An example on how to reproduce this is here.
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Is this a duplicate of MC-131788?

Yeah it is. I spent 30 minutes looking for it but couldn't find it. That means this one gets closed as a duplicate and the one for Bedrock Minecraft stays open.
Relates to MCPE-37860.