Our company's Project Managers often share files with our clients with SharePoint Online, but inevitably, when that client also uses M365, their users will report, after a short while, errors in sharing. Example of errors: -when uploading a document "Sorry, there was a problem uploading this file. Please try again". -when logging in "Sorry, another account from your organization is already signed in on this computer" -"We couldn't open that location. It might not exist or you might not have permission to open it"
The second error seems to point out the issue: it's a conflict between their M365 currently logged in credentials and the credentials on our SharePoint shared files/folders.
My question is, what is the right way to handle this? Please help!
Based on experience when having external access enabled, i always try to group users with groups instead of giving direct permissions on single items. I would suggest creating a seperate space, where permissions are delivered via groups and are not unique and giving site-wide access(read-only). The above approach really handles well.