Our server gets really laggy when we use the plugin. We're using the newest build of Spigot 1.13.

Here's the timings report: https://timings.spigotmc.org/?url=xuwapegise

It used to work fine and without lag, but the last few days it's become very bad. I think maybe Spigot did something to the 1.13 build but it affects this plugin badly.

Hmm, I looked at this before but I guess I didn't have time to comment. Basically, this is 1.13 being very slow, and especially so when converting chunks of the world to the 1.13 block types. You can kind of alleviate this by disabling the chunk cacher in settings.

(There's no way to load chunks asynchronously unless we use Paper, which I may have this feature exclusively use instead.)

Btw, wild version 2.0 does do async chunks so ye, just wait for 2.0 to release.