Microsoft Lync 2013 (Skype for Business) caches proxy resolution for each URL, and doesn't clear the cache immediately after a network change. This can cause a meeting join failure after the network is changed and the proxy is cached.
To fix this issue, install the September 6, 2016, update (KB3118281) for Lync 2013 (Skype for Business).
By default, the fix is disabled after you install this update. To enable the fix, see "Registry information".
Lync 2013 was upgraded to Skype for Business in April 2015.
Important Follow the steps in this section carefully. Serious problems might occur if you change the registry incorrectly. Before you change it, back up the registry for restoration in case problems occur.
After you install this update, you can follow these steps to enable a Group Policy setting to fix the issue:
Start Registry Editor.
Locate and then select the following registry subkey:HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\15.0\Lync
Go to Edit > New > DWORD Value, type ResetProxyResolutionCacheOnEndpointDisable, and then press the Enter key.
Go to Details > ResetProxyResolutionCacheOnEndpointDisable > Modify > Value data, type 1, and then select OK.
Exit Registry Editor.