I used this Command in a Repeating Command Block 1 Block under me:
/tp @e[x=~,y=~,z=~,dx=0,dy=1,dz=0] ~ ~1 ~

Previously tested in Minecraft Java Edition Version 1.12.2, worked as expected. I got teleported 1 block above my position.

When I tested it in Minecraft Java Edition Snapshot 17w46a, I get the following error message:
[xx:xx:xx] Incorrect argument for command at position 3: tp <--[HERE]

When I type the Command in the Chat, an error message will appear in the UI. An Image of this Error Message is attatched to this Bug Report.

I had posted this Bug already, but I was refered to the same Bug in a Minecraft Version of the year 2014. I assume that it was an missunderstanding, because as I already mentioned this had worked in Minecraft Version 1.12.2.