SWM's javaagent makes other plugins not enable properly

Describe the issue
Plugins refuse to load when using java agent on JVM arguments.
Seems to be my fault but I couldn't find how to fix it anywhere else.

Spigot version
WindSpigot 2.1.2 (1.8.8); also tested with unmodified Spigot (1.8.8).

Plugin version
2.2.1

How to reproduce
Set up a server with any plugin, they should load just fine, but when they are enabled they gave me the same error message (shown below), ending up with just Slime World Manager working properly. When I remove the javaagent from the JVM args, SWM plugin and classmodifier, other plugins are enabled correctly.

Crash reports (if available)
[19:40:53 INFO]: [ViaVersion] Enabling ViaVersion v4.8.1
[19:40:53 ERROR]: Error occurred while enabling ViaVersion v4.8.1 (Is it up to date?)
java.lang.NoSuchFieldError: Class javassist.CtClass does not have member field 'javassist.CtClass[] a'
at javassist.f.(Unknown Source) ~[?:?]
at javassist.f.a(Unknown Source) ~[?:?]
at com.viaversion.viaversion.ViaVersionPluginL10.a(Unknown Source) ~[?:?]
at com.viaversion.viaversion.ViaVersionPlugin.onEnable(ViaVersionPlugin.java) ~[?:?]
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:326) ~[server.jar:]
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:332) ~[server.jar:]
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:400) ~[server.jar:]
at org.bukkit.craftbukkit.v1_8_R3.CraftServer.loadPlugin(CraftServer.java:451) ~[server.jar:]
at org.bukkit.craftbukkit.v1_8_R3.CraftServer.enablePlugins(CraftServer.java:409) ~[server.jar:]
at net.minecraft.server.v1_8_R3.MinecraftServer.s(MinecraftServer.java:443) ~[server.jar:]
at net.minecraft.server.v1_8_R3.MinecraftServer.k(MinecraftServer.java:407) ~[server.jar:]
at net.minecraft.server.v1_8_R3.MinecraftServer.a(MinecraftServer.java:367) ~[server.jar:]
at net.minecraft.server.v1_8_R3.DedicatedServer.init(DedicatedServer.java:327) ~[server.jar:]
at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:620) ~[server.jar:]
at java.lang.Thread.run(Thread.java:1583) ~[?:?]
[19:40:53 INFO]: [ViaVersion] Disabling ViaVersion v4.8.1
[19:40:53 INFO]: [ViaVersion] ViaVersion is disabling, if this is a reload and you experience issues consider rebooting.