Prompted to sign in to another tenant

This is happening to a few of our users as well. I do not believe it is a NetDocs issue, but something that NetDocs is doing (prompting authentication) when it runs upon Outlook opening. The tenant we are prompted to log in to is a client and after working through some stuff with the MS Entra team I suspect our client shared a file on OneDrive, SharePoint, or a secure email that prompted our user(s) to login and approve/grant access to that tenant to create a guest account. I am working with our client to see what was shared and how they can stop this from happening.

I'll return here looking for or with an answer. Glad it is happening to others