I've experienced a lot of lag when I hit a NPC and I've been testing every mod for hours and hours. I've discovered that it was MalisisDoors (or MalisisCore).

I can't play in my server with this mod, even the much I liked it :(
I hope someday this mod get fixed!

It's not only me. Someone in the SpongeForge discord had lag in his server too. I told him to remove Malisis and he told me:

YOOOOO WHAAAAAAAAAT
Removing Malisis worked
Like, the ENTIRE lag that I had, just vanished
WTF