Okay, so I was playing in a server with my friends and we wanted to go a little overboard with the raids. We decided to give each other the bad omen effect amplified to 100 to see the ultimate experience. So, while defending a few raids, we saw no pillagers with banners, so we thought it was too high, and therefore broken. We later set the difficulty to peaceful to "end" the raid to our thought. Well, we then thought we should just set the bad omen effect to 2, and go in and out of the village to stack the effects. It was chaotic, still no banner pillagers though. We ended up having to get off midway through the raid so we left the server thinking that we'd resume it later. It didn't work. I logged in, but to my surprise, the raid had "ended" but to a little bit of lag... Not much, but a bit. I decided to shrug it off, and then spawned in evokers, phantoms, ghasts, zombies riding on chickens, elderguardians, ilusioners, and more to simulate the raid for when my friends get back on. But thought it was too much so I set the difficulty to peaceful again, then back to hard. There were chickens all over the ground from the zombies riding them. So I did a kill @e command with type chicken to kill them, but it killed everything instead. This was when I noticed a huge chunk of lag 1st, but freaked out when villagers were killed along with iron golems, though looking back at it, it could have been the pillagers from that time I logged on that I told you about, just while the server was off... But I legitimately don't know. Anyways, I spawned more villagers in hoping we could work our way back up, but it just added to the lag. Anyways, the game was running at 4.75 ticks per second from a debug. And my hypothesis is that the mass stacking of the raids, without them properly ending, or a way to for that matter since the pillagers aren't there anymore, added extra strain on the cpu and therefore made it lag.

side note

we deleted the contents of the raids.dat file to delete all the extra raids, and it fixed the lagging. To fix this in the future, possibly add a way to end raids via a command. One that tapps into this file. Thank You, and Happy Crafting