{Quick Fix} Qualify button on Lead not working in Dynamics 365

I have been working with Customer IT Team on a Dynamics 365 project and we have been doing kind of fancy stuffs, new features and what not. And suddenly we are being reported that Qualify button on lead form is not working. However the same is working from the “Home Page grid”.

First glance and I thought – Must be some silly tampering with the Qualify button. However one quick inspection with Ribbon Workbench negated that suspicion. How can such a stuff working for years can’t work all of a sudden in our environment? Product Bug? Can’t be for sure. It’s been working for years!

After beating around the bush, we finally decided to keep a back-up of our customizations and restored vanilla lead form from different environment. Qualify button started working like piece of cake.

In curiosity, to find out what caused the issue, I started removing one field…