Empty Created By column of items created by a specific user but Modified By is not empty

Created and ran a flow (refer: https://spknowledge.com/2021/03/14/power-automate-how-to-update-author-editor-column/ ) to fill up empty created by column of some items. It works really well. However, there are items from a specific user that after running the flow, both using their email and #EXT#@...onmicrosoft.com one since theyre a guest user, Created By of those items are still empty, but the Modified By is filled up. 

Id like to add that items from other guest users were successful, but it is only this specific user that the Created By is empty.