Thank you for reaching out to us. As I understand you are seeing issues in your Azure AD usernames replaced with numbers, as per the example mentioned in the question.
Would like to check users in question how do they look in metaverse on your AD Connect ( sync) server ?
Any errors on your Sync server that you have noticed ? How many users are impacted by this behavior ?
Let me know if you have any further questions, if needed we can connect offline and troubleshoot on the same.