I've spoken to Microsoft and done testing with them and its deffo not Azure.
But yeah, user is created in SIMS, that goes across to Xporter/IDaaS which then creates their account based off their SIMS information, which links to SDS and such to create Class Teams and such
I'm going to take a look at Xporter to see if there is a field, I've been told by others in my team who have worked for the company longer that Xporter only kicks in on a NEW person adding to SIMS, but... I'm not so convinced that is what is happening.
Thanks for all the ideas everyone!