Some team members only have 1 letter in people column, others have 2

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In my team some people have their 2 initials in eir icon but some only have 1. I am CC and a colleague is TB but another team member is just T. I have changed the ‘picture’ in my profile and it has taken and shows at the bottom left of my page but those changes don’t appear when I select a team member in a People column. Any tips ?