When both the player and the Drowned are standing on waterlogged slabs, the Drowned will not move towards the player.

Steps to Reproduce:
1) Make a platform of 5x5 wooden bottom slabs
2) Waterlog the middle 4x4
3) Place a Drowned in the Waterlogged slab
4) Set your gamemode to survival and stand still on the platform with the Drowned
5) Make sure the time is set to night so the Drowned tries to attack you