Keep getting kicked out of the server

[Tallmess]

here's a small video of what happened. https://streamable.com/57hu4w
Minecraft java version 1.12.2 with mod pack RAD. I basically got hit by a golem's laser beam and it broke my game. Watch the video above to see.
Can anyone guide me through fixing this problem please?
Here's the log of the report:

net.minecraft.util.ReportedException: Ticking player
    at net.minecraft.entity.player.EntityPlayerMP.onUpdateEntity(EntityPlayerMP.java:459) ~[oq.class:?]
    at net.minecraft.network.NetHandlerPlayServer.update(NetHandlerPlayServer.java:173) ~[pa.class:?]
    at net.minecraftforge.fml.common.network.handshake.NetworkDispatcher$1.update(NetworkDispatcher.java:209) ~[NetworkDispatcher$1.class:?]
    at net.minecraft.network.NetworkManager.processReceivedPackets(NetworkManager.java:285) ~[gw.class:?]
    at net.minecraft.network.NetworkSystem.networkTick(NetworkSystem.java:180) [oz.class:?]
    at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:790) [MinecraftServer.class:?]
    at net.minecraft.server.dedicated.DedicatedServer.updateTimeLightAndEntities(DedicatedServer.java:397) [nz.class:?]
    at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:668) [MinecraftServer.class:?]
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526) [MinecraftServer.class:?]
    at java.lang.Thread.run(Unknown Source) [?:1.8.0_271]
Caused by: java.lang.NoClassDefFoundError: net/minecraft/client/Minecraft
    at com.windanesz.ancientspellcraft.handler.ASArtefactHandler.onPlayerTickEvent(ASArtefactHandler.java:519) ~[ASArtefactHandler.class:?]
    at net.minecraftforge.fml.common.eventhandler.ASMEventHandler_146_ASArtefactHandler_onPlayerTickEvent_PlayerTickEvent.invoke(.dynamic) ~[?:?]
    at net.minecraftforge.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:90) ~[ASMEventHandler.class:?]
    at net.minecraftforge.fml.common.eventhandler.EventBus.post(EventBus.java:182) ~[EventBus.class:?]
    at net.minecraftforge.fml.common.FMLCommonHandler.onPlayerPreTick(FMLCommonHandler.java:365) ~[FMLCommonHandler.class:?]
    at net.minecraft.entity.player.EntityPlayer.onUpdate(EntityPlayer.java:190) ~[aed.class:?]
    at net.minecraft.entity.player.EntityPlayerMP.onUpdateEntity(EntityPlayerMP.java:382) ~[oq.class:?]
    ... 9 more