To reproduce:
1. Open project
2. Build scene "scene" to WebGL with fast rebuild

Notice that this warning appears:
UnityEditor.BuildReporting.StrippingInfo must be instantiated using the ScriptableObject.CreateInstance method instead of new StrippingInfo.
UnityEditor.CodeStrippingUtils:GenerateDependencies(String, String, RuntimeClassRegistry, HashSet`1&, HashSet`1&)
UnityEditorInternal.AssemblyStripper:RunAssemblyStripper(String, IEnumerable, String, String[], String[], String, IIl2CppPlatformProvider, RuntimeClassRegistry, Boolean) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/AssemblyStripper.cs:229)
UnityEditorInternal.AssemblyStripper:StripAssemblies(String, IIl2CppPlatformProvider, RuntimeClassRegistry, Boolean) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/AssemblyStripper.cs:128)
UnityEditorInternal.IL2CPPBuilder:Run() (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:201)
UnityEditorInternal.IL2CPPUtils:RunIl2Cpp(String, IIl2CppPlatformProvider, Action`1, RuntimeClassRegistry, Boolean) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:135)
UnityEditor.HostView:OnGUI()

Expected result: it doesn't appear.