This was not an issue in 1.15.2.

Steps to reproduce:

1. /summon area_effect_cloud ~ ~ ~ {Duration:1000000,Passengers:[{id:shulker,NoAI:1b}]}
   /execute as @e[type=shulker] run data merge entity @s {Peek:1b}
   /execute as @e[type=shulker] run data get entity @s Peek

2. See 0b as result; if not continue following the steps.

3. /execute as @e[type=area_effect_cloud] at @s run tp @s ~ ~0.1 ~
   /execute as @e[type=shulker] run data merge entity @s {Peek:1b}
   /execute as @e[type=shulker] run data get entity @s Peek

4. See 0b as result; if not repeat second set of commands up to 10 more times; you're guaranteed to get the Y position where it won't get a non-0 Peek value.