I have a zombie farm with a bubble column that takes them to a 22 block drop. everything around the farm is fine and functional without any issues. However, on 2 different occasions  days or weeks apart.

I went into the bubble column to clear out a stuck zombie and when i landed on the kill chamber i did not lose hearts from the fall, instead i gained additional  golden hearts. 

I do not have any potion effects. one time i had a diamond armour set with enchantments 
unbreaking 3, mending, thorns 2, protection 3, blast protection 3, aqua affinity 1, depth strider 1.

the other time i had full netherite with essentially the same except i also had feather falling and it happened again. 

This bubble column/dropper is the only place i have ever experienced it. it has happened twice  in the exact same spot. seems to be located at the very edge of the dropped where the water goes into the hole and stops flowing at a sign on the wall.  although in my attempts to reproduce i take damage as per normal, it only occurs randomly. Video of it here https://youtu.be/mZQFfr4f6JA .

I don't know if it matters but i am using a warped root sign post where the water goes down  the dropper portion.