Unable to open certain webpages unless IPV6 disabled

I have three Windows PCs - 1 Windows 7 Pro laptop, a Windows 7 Home Prem PC and a Surface Pro (Win 8 Pro).
Lately (the past month or so) I have had trouble opening a couple of webpages, notably en.wikipedia.org from the Win 8 Surface Pro. Sometimes it opens OK, many times it fails to open, with the spinning wheel on the tab. It times out.
The other PCs have no problem opening wikipedia whilst this problem is evident on the Win 8 Surface Pro.
This problem exhibits itself whether I use my default FF browser, or if I use IE as browser - same problem.

If I use Control Panel > Network > Properties and DISABLE IPv6, then wikipedia opens fine right away.
A reboot of the Surface Pro fixes it for a while, but it returns. A reboot of the router (Linksys E4200) also seems to improve the situation, temporarily.

I'm stumped as to the fundamental cause of this intermittent, yet persistent, error.
Anybody else with similar experiences, any advice? All pointers gratefully received. Thanks!