There has been a bug in Essentials since the implementation of this feature.
In Minecraft, if I used the command /tp ~ ~5 ~, I would teleport up 5 blocks.
However, if I run that with Essentials installed, the command would fail.
Now.. If I used /tp ~0 ~5 ~0 in Essentials, the command would then work.
The bug is that you need an integer to suffix the ~.
I believe this defeats the purpose of having the ~ for relative commands, if you still need to add numbers to use it.
I have a simple patch that will allow relative positions to function as desired.

https://github.com/CoolV1994/Essentials/commit/3bcac51ffdf32401a4673b2a9c41cd8ee673f813
https://github.com/CoolV1994/Essentials/commit/9332f9463c5c657b5b5183e6dae665cccceb7d79

Thanks for reading, I would like to see this fix in a future release of Essenrt