Old Combat System Glitch

So I was playing on my Minecraft server, and was fighting a regular zombie, when I realized I wasn't getting the "sweep" effect that swords emit. I also noticed I could spam my attack button. I don't know why or how this occurred. Please try to fix this glitch. Here is the server IP:

stufflolxd.minehut.gg

 

P.S. Please try to fix it without resetting the sever. Me and my friend have worked hard on it.