@ts-lab, Thanks for posting in Q&A. From your description, it seems the Microsoft 365 app previously installed on the device is failed to install the Microsoft app from intone.
Based on my experience, if any office related app is running on the device side will prevent the installation. Please go to Task manager and confirm no office related app is running.
Meanwhile, please ensure the "Remove MSI from end-user devices" is set as yes when we deploy Microsoft 365 app from Intune. Check "Before you start" in the following link to see if all are met.
https://learn.microsoft.com/en-us/mem/intune/apps/apps-add-office365#before-you-start
In addition, we can follow the steps under the troubleshooting to see if more finding can be found.
https://learn.microsoft.com/en-us/mem/intune/apps/apps-add-office365#troubleshooting
Hope it can help.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.