Paper/paper-server/nms-patches/net/minecraft/world/effect/MobEffects.patch

--- a/net/minecraft/world/effect/MobEffects.java
+++ b/net/minecraft/world/effect/MobEffects.java
@@ -47,6 +47,10 @@
     public MobEffects() {}
 
     private static MobEffectList register(String s, MobEffectList mobeffectlist) {
-        return (MobEffectList) IRegistry.register(BuiltInRegistries.MOB_EFFECT, s, mobeffectlist);
+        // CraftBukkit start
+        mobeffectlist = (MobEffectList) IRegistry.register(BuiltInRegistries.MOB_EFFECT, s, mobeffectlist);
+        org.bukkit.potion.PotionEffectType.registerPotionEffectType(new org.bukkit.craftbukkit.potion.CraftPotionEffectType(mobeffectlist));
+        return mobeffectlist;
+        // CraftBukkit end
     }
 }