All Troubleshooting steps / How To:
Step 1: Set the Skype for Business (Lync) client for manual server configuration (see this link)
Step 2: Close the Skype for Business app with the manual server configuration still in place.
Step 3: Clear the cached Lync files from the PC (see this link).
Step 4: Sign back into the Skype for Business client with the manual server configuration still in place.
If issue persists look to escalate ticket