
Hi @Sam Cooley
According to your description, this login issue may be related to authentication and so on.
Currently I suggest you refer to the article: Fix authentication issues in Office applications when you try to connect to a Microsoft 365 service.
You may also go to Control Panel > User Accounts > Credential Manager, below "Windows Credentials" find the related credentials of Office and OneDrive, then remove them.
If the steps above do not work, it‘s best to open a ticket with Microsoft Support to help review your issue and help you test remotely. They will collect related logs to troubleshoot your issue.
Thanks for your understanding.
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