Ribbon Button Troubleshooting Guide

If you ever run into issues with Ribbon Buttons (with regards to visibility or click events) on Dynamics CRM, try the link below.
Apparently Microsoft has a inbuilt Troubleshooting wizard within Dynamics CRM to identify the various issues with Ribbon Buttons.
Follow the steps in the link and hopefully you should get your button working again.

https://support.microsoft.com/en-in/help/4552163/ribbon-troubleshooting-guide

Note : This guide only applies to Ribbon button issues on the Unified Interface