Hi Ricardo,
Thanks for providing all the steps you’ve already done. They will be very helpful in the troubleshooting process.
Since many causes may lead to Lync sign-in issues, I’m sorry that we are not able to provide you with a solution in this post though you’ve already shared with us a lot of information. Thanks for your understanding.
Before we’re able to provide any further assistance, I would like to collect the following information for narrowing down the cause of this issue:
1. I notice that you mentioned “Unable to sign in to Office 365 or Lync” in the subject. Do you mean that you are unable to sign in to either Outlook Web App (https://outlook.office365.com/owa/) or Lync with your Office 365 account? Is the Office 365 account you are using a newly created one?
2. Whether you get any error message when you fail to sign in to Lync. If so, could you provide us with a screenshot of it?
3. Whether you could sign in to Lync on another computer and whether other users in your organization could sign in to Lync on your Mac.
4. Whether the issue persists when you try it in a different network environment.
Regards,
Lee Li