Can't upload new build due to "The apk is signed with different certificate"

It has been many months since we have uploaded a build to our Alpha Channel.  Today I try uploading and get:

'The apk is signed with different certificate than previous version'.

Of course, we have NOT changed our certificate - ever.  Any thoughts on what else could cause this?

Previous uploads were done through the website (deprecated) or the Oculus Platform Tool in Unity.  Trying this build through MQDH.

Any suggestions would really help my blood pressure!