This may be an old bug, but I notieced it in update 1.14.20, when I was designing mob transport system using water streams.

I have done a bunch of testing (mainly in 1.14.30 on my android 8.0 phone, but I hesitate that this is a device based problem) and I found out that: 

Zombies and Villagers are able to stay at the same spot in flowing water stream, if they are heading towards the source of water stream (pathfinding against the flow) - their momentum has the same energy as the flowing water, so they will not move at all until they change the direction of pathfinding.

Drowneds are affected mostly the same way, but sometimes they do not even need to go against water stream.

Strangly enought, this bug does not affect neither the Zombie villagers or Zombie pigmen (and also husks, as I've found out later)

Husks are completely broken. They DO NOT need to even try to move. They are just ignoring the water flow entirely. Or that is what I thought. I find out that they are just for some reason taller that 2 blocks (I was testing it in two blocks high and one block wide tunnel) Husks are currently something like 2.2 blocks high. Within further testing I have found out, that they after all have no issues with pathfinding in water. By their increased high si indeed a problem (check this reddit post I've made: https://www.reddit.com/r/Minecraft/comments/f2df53/i_have_found_out_this_what_i_consider_a_bug_for/?utm_medium=android_app&utm_source=share )

Neither of these issues apply to the baby versions of these mobs.