Paper/paper-server/patches/sources/net/minecraft/server/ReloadableServerRegistries.java.patch

--- a/net/minecraft/server/ReloadableServerRegistries.java
+++ b/net/minecraft/server/ReloadableServerRegistries.java
@@ -64,6 +64,7 @@
     ) {
         return CompletableFuture.supplyAsync(() -> {
             WritableRegistry<T> writableRegistry = new MappedRegistry<>(type.registryKey(), Lifecycle.experimental());
+            io.papermc.paper.registry.PaperRegistryAccess.instance().registerReloadableRegistry(type.registryKey(), writableRegistry); // Paper - register reloadable registry
             Map<ResourceLocation, T> map = new HashMap<>();
             SimpleJsonResourceReloadListener.scanDirectory(resourceManager, type.registryKey(), ops, type.codec(), map);
             map.forEach((id, value) -> writableRegistry.register(ResourceKey.create(type.registryKey(), id), (T)value, DEFAULT_REGISTRATION_INFO));