As of current, Lithium will throw out errors in combination with Aristois due to entity collision mixins. Aside from completely removing Lithium, there is a temporary fix for this which includes disabling the mixins on Lithium's end. It is unknown what effect this has on the mod's performance.

Steps to disable the mixins:

1. Locate the lithium.properties folder in the config folder of your Minecraft directory. (\.minecraft\config\)
2. Open the file with a text editor (Notepad is fine).
3. Add a line at the bottom of the file and put this in:

mixin.entity.collisions=false

Here's an example of what your config could look like:

Save the file and just like that you can use Lithium with Aristois!

thanks to Dragonruler6008 for this solution!