Unauthorized nickname being used by operation system.
Periodically, but not always, in the 'sent by' field in Apple Mail or Messages - instead of displaying my name or email address, it displays a nickname I didn't authorize. I've asked Siri "call me [my name]" and she says she'll continue to call me [my name] - she does not mention the nickname. The unauthorized nickname is not on my contact card anywhere. This happens for my personal gmail address being used through Apple Mail and not my work or any other email addressed used on through Apple Mail. This can also happen in the Messages App on my Mac or on my iPhone.
It can go years without happening and then will happen again.
Thanks for any help.
iPhone SE, iOS 17