Facebook login failure on InsTube could be due to various reasons such as outdated app version, network connectivity issues, or changes in Facebook's authentication system. Users experiencing login failures should ensure they have the latest version of the InsTube app installed, check their internet connection, and verify if Facebook's login service is operational. Additionally, clearing the app cache or reinstalling the InsTube app may help resolve the issue. If problems persist, contacting InsTube's customer support for further assistance is recommended.