Built a defense system using rail gun turrets. Works perfectly against normal armor, but the ReWIRED mod features a kinetic deflector (that Stops Incoming Projectiles at the cost of power, https://minecraft.curseforge.com/projects/rewired). It seems when the rail gun fires at a player using this specific implant, something is done to the ferro slug that the server doesn't like, causing it to immediately crash.
crash-2018-08-25_20.45.57-server.txt

This crash because there is probably a missing null pointer check in ReWIRED.
Gonna leave this open until it is fixed, though.

I'll try to open a report with them as well then

ReWIRED is putting out a mod update shortly. I'll test it when it drops and if it's working then I can close this one out

Got the new updates from both of you, should fix this issue, thanks!