You share a Azure RMS protected document with one user firstname.lastname@example.org. If you now remove that user and add Samsung@haukeberg.com
-> What happens?
Each share on the file creates a new instance in Azure RMS, hence if you want to remove user email@example.com access you need to revoke access to the document completly.
Note: once you revoke access to a document, all the users will loose access.
Hence if the user firstname.lastname@example.org quits and you revoke access to a document which also Samsung@haukberg.com has access to then both loose access.
Workaround would be to always share a document with as few as possible each time.