The bug
It looks like you are diving up faster in downwards flowing water when there are non-opaque solid blocks next to you.
How to reproduce
Create a one wide hole inside an opaque block and put water at the top
/fill ~1 ~ ~1 ~3 ~5 ~3 sandstone hollow /setblock ~2 ~5 ~2 flowing_water
Go to the bottom of the hole and dive up
Repeat the steps for a non-opaque solid block
/fill ~1 ~ ~1 ~3 ~5 ~3 glass hollow /setblock ~2 ~5 ~2 flowing_water
→ ❌ You dove up faster
Any one also meets the same bug?