Consider the following scenario:
You sign in to Microsoft Lync 2013 on a computer in a network environment.
The environment is deployed with the remote access service or with the IT tools that temporarily blocks network traffic for device validation.
The computer disconnects and then reconnects to the network.
In this scenario, Lync 2013 may take a long time to sign in.
When the computer connects to the network, Lync 2013 tries to download the metadata files immediately. However, the network traffic is not enabled by the IT tools or the remote access service. Therefore, the metadata files fail to download and Lync 2013 caches the failure for several minutes. Therefore, Lync 2013 cannot sign in immediately after the Internet access is enabled.
To resolve this issue, install the following update:
2880474 Description of the Lync 2013 update: April 2014