Ribbon Workbench -- custom button intermittent show issue

Hi,

A customer has reported that since the upgrade to CRM 2016, they've experienced that a custom button which should only appear in the Views ribbon for both the Account & Lead entity, now sometimes doesn't appear in the Lead entity.  Note the issue is intermittent so sometimes it works as expected, however there are periods in the day where it wont appear.

So, instead the custom button will appear in the Account View ribbon and other entities including Contact/Case/Opportunity entity.

Some assistance would be great with this.

Thanks