AEM Common Issues

• AEM Chrome extension  - This browser extension can be leveraged in non-production environments to debug why the UI is slow or broken.  The extension allows you to view the sling request processing (filters executed, which servlet, error handlers, components, sling resources, etc). and any JCR queries that are executed during the page load.
• Touch UI XRay Mode for debugging - This is a tool for debugging Touch UI element issues in non-production environments, it assists in identifying which resources belong to various UI elements. 
• Debugging client-side issues in the Touch UI - Various steps in debugging client-side issues.
• Using AEM Developer Mode to debug component issues - Useful when debugging components during development or in non-production environments.
  

• AEM SItes
  • How to optimize site performance.
  • How to optimize site caches.
• AEM Assets: Tuning Guide.

See this guide on how to debug common critical issues.