Update : While the problem with that one specific email id continues to exist, I have been able to get that employee on to Teams by creating an alias email id and signing up with that email id.

I had to use a completely different browser (Chromium) and an incognito window to get that sign up working.

However I would really like to have this issue actually resolved and not have a symptomatic relief. So if someone can help me get to the root of the issue with that one particular email id, it would really help.
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