Note: This version is basically the same except that Spigot fixed the bug, so I don't have to use the broken workaround anymore. However this means you need a recent build of Spigot which contains the fix.
The rest of this post is mostly copied from the 0.21.0 release:

The config file was changed, you should either delete your current config or add the changes manually, you can see them here: https://github.com/Olexorus/WitherAC/commit/d5e9ac44099faa45b922c6c4605c4c5b9e6ca0f9

Even if I can't actively work on WAC at the moment I'll of course still update WAC to the latest Minecraft version so you can keep using it when your server switches to 1.16

As a bonus I'll also release some other features that I worked on a while ago and didn't have time to release yet.

Changelog 0.21.2:
- updated to 1.16
- added an entity speed check
- drastically improved the high jump / jetpack detection logic, previously it was possible to jump 5 blocks high, now not even 2 blocks are possible
- found a much, much better workaround for Spigot's inconsistent event handling which allowed me to clean up a lot of code and should also fix a few bugs
- performance optimizations and code cleanup