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Dear xavierbe89,
Thank you for posting your query in our community.
Please don't worry, let's resolve your concern together and move towards a path towards resolution.
We would like to explain that this favorite tab is working for single user only. When you Mark a site as favorite It is only marked on your own end. It does not apply to all the other users, if the if they want to make this appear under favorite they need to mark as favorite on their end. That is why there are always different for different users.
If you have any additional questions or if you need any additional help regarding this or anything else at all - let me know, I'll be here to help you out.
And in the meantime, I hope you'll have a lovely day ahead, stay safe & take care!
Yours sincerely,
Sophia