Mike M

I dont see this issue being a duplicate. Planting crops now is a nightmare as gaps are regularly left.

I'm also having this issue.   Also a 3rd gen iPad running iOS 9.3.5.

I've tried factory resetting the iPad and the problem persists.

No idea, haven't played Minecraft in almost 2 years

What sound card youre using? 🙂

Here's a video showing this: Bug

Also turns out this bug occurs sometimes and only my second attempt worked.

Posting to confirm for ghasts and bats in 1.11.2. Neither movementSpeed or speed/slowness effect/potions will alter their movement speeds:

/summon bat ~ ~1 ~ {Attributes:[{Name:generic.movementSpeed,Base:0.001}]}
/summon bat ~ ~1 ~ {ActiveEffects:[{Id:2,Amplifier:5,Duration:19980,ShowParticles:0b}]}
/summon ghast ~ ~1 ~ {Attributes:[{Name:generic.movementSpeed,Base:0.001}]}
/summon ghast ~ ~1 ~ {ActiveEffects:[{Id:2,Amplifier:5,Duration:19980,ShowParticles:0b}]}

Oddly, it seems to work for blazes, but only when they're "walking" (touching the ground)

This appears to still be an active issue in 1.11.2. The command has changed due to Minecraft's updated entity handling, but the overall problem remains.
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Updated command:
/summon potion ~ ~5 ~ {Potion:{id:"minecraft:splash_potion",Count:1,tag:{Potion:"minecraft:harming"}}}
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I've also tried adding in various combinations of the "ownerName" and "UUID" tags to see if that solved the problem, to no avail:
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/summon potion ~ ~5 ~ {ownerName:USER,Potion:{id:"minecraft:splash_potion",Count:1,tag:{Potion:"minecraft:harming"}}}
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/summon potion ~ ~5 ~ {UUIDLeast:0L,UUIDMost:1L,Potion:{id:"minecraft:splash_potion",Count:1,tag:{Potion:"minecraft:harming"}}}
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/summon potion ~ ~5 ~ {UUIDLeast:0L,UUIDMost:1L,ownerName:USER,Potion:{id:"minecraft:splash_potion",Count:1,tag:{Potion:"minecraft:harming"}}}
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(Sorry about the strange spacing, I can't seem to get the formatting to look decent)

@Skylinerw
Thanks! I'll have to look up more about the "modifiers" bit, bit at least this works.

This is disappointing; being able to summon a mob with slowness via active effects would allow for a temporary effect without having to manually modify the entity's movementSpeed attribute later.