This would be a result of unstable internet connection. Make sure your router/access point is not rebooting periodically and your PC has a stable internet connection.
The miner connects to the pool and keeps a connection alive at all times. When your network drops the connection is lost and miner will not really reconnect but establish a new connection.
In some rare cases it could also be an ISP problem with the upstream network.
Check the event viewer, these should be a clear message from Windows indicating a connection drop.