As the title states, when a drowned is in its swimming animation and is knocked out of the water, it has the chance to retain its swimming animation and will not be able to jump.

Steps to reproduce
1. Get a drowned in its swimming animation
2. Get the drowned to try to attack you while you are on land
3. Knock the drowned out of the water. An explosion will usually work.

I have not been able to reproduce it, but I have screenshots of it happening