After you've run your first speed test, try unplugging your internet modem and router. After about 15 secs plug them back in and wait for them to connect properly and run another speed test. You have obviously had good enough speed previously in order to run Netflix without it constantly buffering so your internet modem might also be getting ready to go. Once you've run the speed test and if you are getting the speed your provider promised the problem could be on the Netflix end. I've had it happen a couple of times even though I was getting 50mbps download speed on my test. If you are not getting the speed you are paying for contact your internet provider.