Players are having big lag spikes, but TPS remains at 20.

[Merceric]

Hello, lately some players on my server are reporting big connection lag spikes, I found that villagers are part of the problem, so I installed Villager Lobotomizatornator ( https://www.spigotmc.org/resources/villager-lobotomizatornator.83355/ ), VillagerOptimizer ( https://www.spigotmc.org/resources/villager-optimiser-1-14-2-1-16-3.68517/ ) and FarmLimiter ( https://www.spigotmc.org/resources/farm-limiter.1419/ ). But the problem still persist. Any help with this?

These are my timings: https://timings.aikar.co/?id=5e01e51cc7674591a546607e40f11a26

 

[BurntValentine]

Does it effect all players, or just certain players?

If the TPS is stable and nothing is being flagged in the timings, it's unlikely to be a server-wide if it's not effecting all players at the same time.
If it isn't effecting all players then it could be something in the area they are logging into (ie excessive mobs, particles, item drops, tile entities etc... in the area that their client is struggling to render efficiently) or if it happens anywhere in the world and not in specific spots and seems to be when connecting, not so much during ongoing gameplay.
It could be something that specifically runs on logins such as AuthMe. It could also be them not using the same client version as your server as I can see ViaBackwards and ViaVersion in your plugin list - the more information given regarding the instances that lag happens to find similarities the better in isolating the cause, as pretty much anything can cause lag.