No Custom Plugins under Apps Button Showing

Is anyone else seeing a discrepancy in OWA (Outlook web version) where some people in the org see the Apps button and some see the Add-ins button instead? 

 

One of our custom add-ins is not available via the Apps button, but works fine if you can see the Add-ins button. We redeployed the add-in and it appears in both the Add-ins & Integrated Apps sections of our MS365 Admin.

 

Here's our ribbon for a new message with the Apps button

And here it is with the Add-ins button

 

 

Any suggestions to get the Add-ins button to appear (or a custom add-in in the Apps section) will be appreciated. We've been through many, many iterations of global settings, different browsers, different machines and various real and test user accounts. We have yet to find out how or why a given account sees one or the other, though they do consistently see just one, and never the other.