This problem is a result of the way the Server service and system cache interact on some configurations.
You can try to tune the Server to dedicate more memory to the system cache:
1. Control Panel / Network / Services / Server / Properties / Configure.
2. If Maximize Throughput for File Sharing is selected, try using Maximize Throughput for Network Applications or Balance.
3. If you changed anything in step 2, shutdown and restart.
See tip 0200.