Yogbox 2.0 modpack/server problem.

So , basically , when I start a completely new server of yogbox 2.0 , new map , new everything , everything is fine , no problems.
So then I stop playing with my friend since its late so we can continue tomorrow , the thing is , the second time I load the server , we are invicible , the additional hearts that we get are always empty and unless a mob gives us a 1 shot kill , we are invecible which shouldn´t be the case , basically , we are unable to receive damage since it heals right after I suppose.