What determines the availability of unload / reload buttons for editor modules?

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I’m analyzing the same issue.

In UnrealEngine\Engine\Source\Developer\ModuleUI\Private\SModuleUI.cpp I found the code below. This code is for the module window.

else if ( ColumnName == "ModuleActions" )
			{
				...
				// Reload button
				+ SHorizontalBox::Slot()
					.AutoWidth()
					.Padding( 2.0f, 0.0f )
					[
						SNew( SButton )
						.Visibility( Item.ToSharedRef(), &FModuleListItem::GetVisibilityBasedOnReloadableState )
						.Text( LOCTEXT("Reload", "Reload") )
						.OnClicked( Item.ToSharedRef(), &FModuleListItem::OnReloadClicked )
					]

And If follow the code in the same file, finally I can meet the function GetVisibilityBasedOnLoadedAndShutdownableState() through GetVisibilityBasedOnReloadableState()

EVisibility SModuleUI::FModuleListItem::GetVisibilityBasedOnLoadedAndShutdownableState() const
{
	if ( GIsSavingPackage || IsGarbageCollecting() )
	{
		return EVisibility::Hidden;
	}

	const bool bIsHotReloadable = FModuleManager::Get().DoesLoadedModuleHaveUObjects(ModuleName);
	const bool bCanShutDown = ( FModuleManager::Get().IsModuleLoaded(ModuleName)
								&& !bIsHotReloadable 
								&& FModuleManager::Get().GetModule(ModuleName)->SupportsDynamicReloading() );

	return bCanShutDown ? EVisibility::Visible : EVisibility::Hidden;
}


EVisibility SModuleUI::FModuleListItem::GetVisibilityBasedOnReloadableState() const
{
	return GetVisibilityBasedOnLoadedAndShutdownableState();
};

This function checks DoesLoadedModuleHaveUObjects() . I think that Having UObject or Not can affect the visibility of reload button.