That's not the actual directory, you have to replace /mcversion/ with the mc version. If you're trying to use the run command to find it, it would be %appdata%\.minecraft\libraries\EMC\VERSION\configs
Can you please still send an IP that it occurs on, and also see if it occurs with Singleplayer
Aristois is not a ghost client. Servers will see you running vanilla if you use Fabric, but if you use Forge they can see that, and which forge mods you have
Most likely a mod conflict. You can read the known ones here: https://aristois.wiki/modpacks/forge#C4 otherwise send the list and I can see if any stick out
If doing any of the above does not help, please upload your config file. Use the command .config export and then upload the config to https://easyupload.io/
And include the server IP
You can do the command in singleplayer, remove optifine, or you can just copy the file from .minecraft/libraries/EMC/(mc version)/configs/