S/MIME functionality available in Outlook for iOS TestFlight

Ross Smith IV - Hoping you might give us a hand, support hasn't been responsive.

Our S/MIME certs through DigiCert are manually installed in devices and published to GAL.

We're recently attempting to move from iOS Mail to Outlook but are running into intermittent functionality.

Sending an initial encrypted/signed email to anyone with a cert in GAL seems to work fine. Furthermore, replying to encrypted/signed emails sent from other iOS Outlook users seems to work. The problems seem to occur replying to some messages sent from desktop for some mobile users. 

When my teammate sends an encrypted/signed message from his desktop, I'm not able to reply on mobile (send greyed out), despite his cert being correct in GAL and replying to his messages sent from mobile work fine. My boss, however, can reply to these same messages successfully, despite no apparent difference in our configuration. 

It would be really helpful for troubleshooting to view the Microsoft publisher keychain in iOS, in order to see what our local cache looks like vs. GAL or other's local caches - but I can't seem to find a way. Is there any user interface available for this?

Thanks, any tips or info would be much appreciated. Happy to provide any more information that might help.