Okay, to put it in bigger detail, I have a forge server running for a modpack I made myself. I run forge with 4G of ram, I have about 50 mods. Everything should be fine.
I check my tick speed, everything seems fine. Averaging at around 0.500tps. But whenever I join the server myself, it goes shooting up at 20, 40.000tps.. why does this happen every time I join my own server? Of course, whenever I leave, it drops like a rock back to below 1.