Error in console:
Error occurred while enabling OldCombatMechanics v1.6.0 (Is it up to date?) java.lang.NullPointerException: null at gvlfm78.plugin.OldCombatMechanics.SpigotUpdateChecker.run(SpigotUpdateChecker.java:75) ~[?:?] at gvlfm78.plugin.OldCombatMechanics.SpigotUpdateChecker.<init>(SpigotUpdateChecker.java:49) ~[?:?] at gvlfm78.plugin.OldCombatMechanics.OCMUpdateChecker.<init>(OCMUpdateChecker.java:28) ~[?:?] at gvlfm78.plugin.OldCombatMechanics.OCMMain.registerAllEvents(OCMMain.java:120) ~[?:?] at gvlfm78.plugin.OldCombatMechanics.OCMMain.onEnable(OCMMain.java:54) ~[?:?] at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:264) ~[minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:337) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:402) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at org.bukkit.craftbukkit.v1_12_R1.CraftServer.enablePlugin(CraftServer.java:380) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at org.bukkit.craftbukkit.v1_12_R1.CraftServer.enablePlugins(CraftServer.java:329) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at org.bukkit.craftbukkit.v1_12_R1.CraftServer.reload(CraftServer.java:751) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at org.bukkit.Bukkit.reload(Bukkit.java:525) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at org.bukkit.command.defaults.ReloadCommand.execute(ReloadCommand.java:25) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at org.bukkit.craftbukkit.v1_12_R1.CraftServer.dispatchCommand(CraftServer.java:647) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at org.bukkit.craftbukkit.v1_12_R1.CraftServer.dispatchServerCommand(CraftServer.java:633) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at net.minecraft.server.v1_12_R1.DedicatedServer.aP(DedicatedServer.java:444) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:407) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:679) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:577) [minecraft_server.jar:git-Spigot-5340a52-27b8bf9] at java.lang.Thread.run(Thread.java:745) [?:1.8.0_74]

Config:
https://pastebin.com/RsD2XRYR
Version:
1.12.1-R0.1-SNAPSHOT
OCM:
v1.6.0

Try setting the update checker in the config to bukkit. I don't know what happened to the spigot update checker but it appears to be broken.

Changing it to bukkit does not work nor does putting it to false. Seems to do it for all versions now, new and old.

Can you please try with the latest test version

Latest dev build fixes the problem.