So some background information is I am trying to create a slime that has a custom block texture with it, and the best way I am attempting to do that is to teleport an armor stand to the slime, then one below it very rapidly. I first summon them by using a custom named endermite:

/execute @e[type=Endermite,name=Spawn_Battle_Sentry] ~ ~ ~ /summon Slime ~ ~ ~ {CustomName:"Battle_Sentry",CustomNameVisible:1,Size:1,Attributes:[{Name:generic.knockbackResistance,Base:2}],PersistenceRequired:1,ActiveEffects:[{Id:14,Amplifier:0,Duration:20000000}]}

/execute @e[type=Endermite,name=Spawn_Battle_Sentry] ~ ~ ~ /summon ArmorStand ~ ~-1 ~ {CustomName:"Battle_Sentry",CustomNameVisible:1,Invisible:1,Invulnerable:1,NoGravity:1,Equipment:[{},{},{},{},{id:stonebrick,Damage:2,Count:1,tag:{display:{Name:Sentry Stone}}}],DisabledSlots:2039583}

The commands shown here all run on a fill clock (20 times per second), and the endermite is killed directly after summoning those two entities. The following commands are then run after in the fill clock order:

/execute @e[type=Slime,name=Battle_Sentry] ~ ~-1 ~ /tp @e[type=ArmorStand,name=Battle_Sentry,c=1,r=2] @e[type=Slime,name=Battle_Sentry,c=1] 

/tp @e[type=ArmorStand,name=Battle_Sentry] ~ ~-1 ~

They are made that way to support multiple slimes summoned to be custom-looking ones to exist. When finished on the loop they look like the third image (I was in gamemode 3 to show the positioning).
The first problem is that when the second command's y coordinate is changed to any number, before summoning the endermite, to something like -3, the armor stand will still render like it is only one below the slime. The issue then is when I change it back to -1, the armor stand will move upwards and render like it's being teleported to one above the slime. Exiting from the singleplayer world and coming back can either fix the issue, or make it look like image 2.

The second issue is when trying to make sure a set of two of these entities don't have their armor stand teleport to another slime that it's not supposed to, (It really does seem impossible to make them not when they get too close, but that's not the problem, that's more of a lack of ability to do so), I change the first teleport command to the following:

/execute @e[type=Slime,name=Battle_Sentry] ~ ~-1 ~ /tp @e[type=ArmorStand,name=Battle_Sentry,c=1,r=2] @e[type=Slime,name=Battle_Sentry,c=1] 

And this can sometimes create another rendering glitch that makes it look like the first image, where one armor stand is on the slime, and another is where the previous slime was, but it moves like it's a match of the first armor stand in a different place, and exiting and coming back to the world makes it so the armor stands stop looking like that and look like they are both being teleported to one below the slime.