Sharing issues with Sharepoint Online when the other Org also uses SharePoint Online

Regular Visitor

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!

1 Reply

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.