Levitation Effect Not Consistent

I am currently using minecraft 1.14.4, and when I apply levitation to a group of armorstands with shulkers riding them, they all start levitating at different times.

The command I am using:

/effect give @e[type=minecraft:armor_stand] minecraft:levitation 5 5 true

Here is an image:

I was wondering if anyone knows why this happens and if there is a fix for it.

This seems to be an issue with the movement interpolation between server ticks. The Minecraft client not only shows the armour stands at the 20 positions they have per second, it instead calculates more in between, to show a smoother movement for higher framerates than 20.
Apparently this does not work quite right with high speeds. It happens in both 1.15.2 and the latest snapshot as I'm writing this (20w08a). I created a bug report for it for now: https://bugs.mojang.com/browse/MC-172870
…but I'm sure it's a duplicate of some other report. It's hard to search for something like this.

This effect is only visual, running

/execute as @e[type=armor_stand] run data get entity @s Pos[1]

reveals that they are in fact all on the same height.

Workaround: Reload the world. That makes all armour stands that were summoned before reloading the world work properly.