I had the same problem.
If you have a router from TP-Link, D-Link, ASUS or maybe a router produced by some other companies
then this is a problem with a router.
There are two ways to solve this problem:
1) Upgrade firmware for your router. You may download the last version of firmware
from website of the manufacturer of your router.
2) Change "MTU" value to "1400" in your router settings.
This option is located in "IP Config" -> "WAN & LAN"