Okay. I have been banging my head against the wall with this issue for a couple days now, and I believe I have found a fix - or more likely a work around. I don't 100% understand why it works, or why it was a problem, but... For me the problem seems to be related to IPv6. I turned off IPv6, and everything is 100% back to normal. If you google "turn off ipv6 windows 10", you'll find instructions to do so, many of them registry edits. I, however, just went to the "Network and Sharing Center", and under "view your active networks" i clicked on "Connections: Ethernet" (might not be ethernet on yours), then clicked properties, then unchecked "Internet Protocol Version 6"...
That said, this was mega weird for me. I installed Windows 10 on 2 pc's in my home. Had the same problems with both. Thinking I may be having some really odd problems with browser compatibility or somethign, I reverted to the copy of Windows 8 which had previously worked flawlessly. Full reformat, and the problem persisted in Windows 8! Still makes no sense to me.