In SharePoint, site owners can send invitations to external guest, it’s not very common but somehow the guest account might get deleted from the SP Site, because of wrong permissions given..ect.
Because of the permission issue, the user then gets deleted from SharePoint and Azure AD. Site owner then sends a new invitation the the guest, and thing seems fine but the guest will get an error stating “we cannot find your firstname.lastname@example.org” in tenant SharePoint directory.
This is actually caused by the fact that, if the guest account gets deleted from Azure AD, it won’t be permanently deleted at once, retention is default 30 days, and the account will be in the deleted list, meaning when the owner sends a new invitation the guest never get the chance to re-register the account to the host Azure AD directory.
**Note to self**
If guest users gets error stating the account is not found in the directory, verify that it’s not in the “deleted” list.