One of our users believes they have discovered an issue with onward sharing of links. I've not attempted to reproduce myself.
If they onward share from the desktop app (Word), the person attempting to share it on gets a message that it has been referred to the owner for permission, and the owner gets an email. This is the behavior we want and expect.
However, if the onward share is done from the browser version of Word, it just goes direct to the 3rd party, with no notification and no request to change permissions.
Only tested from Word so far. All parties involved are internal to the organisation.
Not sure if I understand correctly, but if you mean re-sharing of documents by people that have been granted access to them, this is the expected behavior (for people with Edit permissions). You can disable it via PowerShell.