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Hi Natstj,
Did you modify the file only by yourself, or did you collaborate the file with others?
refer to Office Online – Versioning behavior while in co-authoring state. To make a summary how version created by different scenarios:
1. If you are alone in a workbook, make a change, flip to Reading View (leave Editing View), you will immediately see a new version. All changes before closing this file will be saved to this version.
2. If there are multiple people in the co-authoring session, everyone needs to leave before you see the new version.
If you collaborated the file with others at that time, you may see a later time because the time should be when all users closing this file.
Regards,
Rena