cardboard VS Tuinity

Are you mixing up PaperMC with Fabric? PaperMC indeed is a fork of Spigot that is performance oriented. Fabric is a Modloader just like Forge. Fabric does not have plugin capabilities, since it is Mod based. There are Projects, that aim to add plugins to Fabric, like Cardboard, but these are still a work in progress. As you can see by their Progress Tracker.

I play strictly vanilla Minecraft, and use paper to host my servers, so this may be out of my territory, but I do remember Cauldron being popular for Forge mods and spigot plugins, so maybe give this a go?

The two pinned issues on their github show how much has yet to be implemented. Just as an example, here's the list of events and see how many are unchecked.

I believe it's a mixin conflict between Create and Cardboard: https://github.com/CardboardPowered/cardboard/issues/350

As for Spigot plugins on a Fabric server, Cardboard does work, though it’s still in beta and incomplete.

Use Cardboard: https://github.com/CardboardPowered/cardboard

Some more detail on how the server internals will work: The server is a based on Cardboard which allows both fabric mods and bukkit/spigot plugins to run at the same time, along with datapacks of course. The server has a wide variety of lag reduction and bugfix mods, as well as some rudimentary anticheats to prevent xraying and other blatant unfair advantage hacks

Cardboard exists but from my experience it can be buggy: https://cardboardpowered.org . Use at your own risk!

Could also pregenerate your world with chunky. To make it quicker add Starlight, Lithium, tic-tacs(This might be incompatible with some worldgen mods, but it massively speeds up terrain gen speeds if it works), and Carpet(use the "/tick freeze" command to freeze the game so there's more resources for terrain gen). Then switch to a paper style Tuinity server and set the worldborder to keep people from moving past pregenerated chunks.

You can try out Tuninty for extra performance

Tunity - Github Repo - (no website)

Strip out all plugins, make backups of & reset your yml's. Does the bug still occur after doing that? Then report on their issues tracker: https://github.com/Spottedleaf/Tuinity/issues

Tunity: https://github.com/Spottedleaf/Tuinity

Tuinity is a fork of Paper that includes optimizations that are generally tailored for servers with high player counts. It also includes Starlight: a complete rewrite of the lighting engine which greatly improves the speed of chunk generation. One benchmark has shown that Starlight can generate light 35x faster than vanilla.

Tuinity

For server jar I would recommend using Tuinity (or maybe even Purpur). As Tuinity has some more optimizations that help for larger servers and Purpur is a fork of it that I believe has even more experimental optimizations.

https://github.com/Spottedleaf/Tuinity/blob/master/patches/server/0061-Rewrite-the-light-engine.patch here is the patch, at the top he writes a description that can help you read more about it.

Use Tuinity (it's a fork of Paper, optimized for higher play counts)