That issue has been experienced by me too. In a Samsung Service Center, when contacted a technician told me that after inserting a sim in slot 1 if it shows a different number then just tap the shown slot and rename option will appear and rename it as slot 1. Check it in your handset. If it works, please click the 3 dots beside my comments and acknowledge it as resolved.
We would like to inform you that this is not a bug or issue, it is the normal concept of the latest update. In previous versions of One UI, some SIM information was linked to the SIM card itself, while other information (such as the name and icon) was associated with the slot.
However, starting with One UI 7, all SIM information, including the name and icon, is now tied to the SIM card itself.
