try the fix

Author: Vighnesh-V

Analysis/include/Luau/FragmentAutocomplete.h

@@ -75,7 +75,6 @@ struct FragmentAutocompleteResult
 {
     ModulePtr incrementalModule;
     Scope* freshScope;
-    TypeArena arenaForAutocomplete;
     AutocompleteResult acResults;
 };
 

Analysis/src/FragmentAutocomplete.cpp

@@ -1658,21 +1658,21 @@ FragmentAutocompleteResult fragmentAutocomplete(
     auto globalScope = (opts && opts->forAutocomplete) ? frontend.globalsForAutocomplete.globalScope.get() : frontend.globals.globalScope.get();
     if (FFlag::DebugLogFragmentsFromAutocomplete)
         logLuau("Fragment Autocomplete Source Script", src);
-    TypeArena arenaForFragmentAutocomplete;
+    unfreeze(tcResult.incrementalModule->internalTypes);
     auto result = Luau::autocomplete_(
         tcResult.incrementalModule,
         frontend.builtinTypes,
-        &arenaForFragmentAutocomplete,
+        &tcResult.incrementalModule->internalTypes,
         tcResult.ancestry,
         globalScope,
         tcResult.freshScope,
         cursorPosition,
         frontend.fileResolver,
         callback
     );
-
+    freeze(tcResult.incrementalModule->internalTypes);
     reportWaypoint(reporter, FragmentAutocompleteWaypoint::AutocompleteEnd);
-    return {std::move(tcResult.incrementalModule), tcResult.freshScope.get(), std::move(arenaForFragmentAutocomplete), std::move(result)};
+    return {std::move(tcResult.incrementalModule), tcResult.freshScope.get(), std::move(result)};
 }
 
 } // namespace Luau