The bug
When an area effect cloud is teleported, it looks to the client as if the cloud wasn't teleported, while it actually changed its position.
How to reproduce
Enable
F3+B
Run
/summon minecraft:area_effect_cloud ~ ~ ~ {Duration:1000s}
Go some blocks away
Notice that there now is a white line where you stood (that's the area effect cloud)
Run
/teleport @e[type=minecraft:area_effect_cloud] ~ ~ ~
Notice that the white line did not move
Close the world and re-enter it
Notice that the white line now changed its position
Original description
I can't teleport an area_effect_cloud
Summon area_effect_cloud:
/summon minecraft:area_effect_cloud ~ ~ ~ {Duration:100s}
Try to teleport:
/tp @e[type=area_effect_cloud] ~ ~1 ~
/tp @e[type=area_effect_cloud] ^ ^ ^1
/tp @e[type=area_effect_cloud] @s
Linked issues
Comments

Why shouldn't the client be informed? Or is there another bug report about it not being informed (did not find anything)?

To be really direct: this report says it’s unable to teleport, that’s not true.
Client not being informed of the cloud position is another issue, and more than likely done for optimization (as the cloud doesn’t move in any way without commands).

But that shouldn't be, right? 'Cause I'm using it for raycasting so it shall execute a command from another location. Also I can't orientate it as I'd like to.
I reopened the report and updated the description and the summary to better reflect what this issue is about.
Apparently, in 1.12.2, it is not possible to teleport an area effect cloud at all.

@unknown that I cannot confirm: I moved area effect clouds in 1.12 a lot.
Ah. I checked again. I totally forgot that /tp
was relative to the target in 1.12.2. That being said, confirmed in 1.12.2 as well.

Try adding an effect to the cloud. Maybe something will change.
No, if the cloud has an effect, nothing changes at all.
It does teleport, client is just not informed about it's new position.