Issues like that (frozen playback that either resumes or stops and returns you to the previous view) are almost always caused by data delivery failures. In other words, it can't read from "disk" (which, in your case, is the network share).
I'd check for:
1. QNAP issues and firmware updates with Windows 8/8.1 (as Jim suggested).
2. General network issues. You didn't specifically mention if you were using a Wireless or Wired network connection. Wireless, of course, can be very difficult to diagnose and issues can be transient (caused by things as weird as "when you run your blender, it dies"). Stress test your network:
http://www.smallnetbuilder.com/lanwan/lanwan-basics/31220-how-fast-is-your-network-five-ways-to-measure-network-speed3. Bad cabling if you have a wired network. These issues can be transient (I've had it personally, more than once).
4. Driver issues on the PC. This is particularly likely if you're using onboard LAN ports made by Realtek and other "cheap" brands. Check for driver updates from the maker of your laptop, not just Windows updates ones which provide only basic functionality.
3. Disk trouble on the QNAP appliance. If it has any verification tools to check for disk trouble, run them.