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This is an ongoing problem and happens on a regular basis - On average, recurring about every 7-10 days.
Like you, I always test it against other independent web sites just to be sure it's a problem with this site and not with the internet or my individual system, and it's always this site.
The most common problem is not the loading of the main index but loading of any other pages subsequently. It can also time out when loading a quote when wanting to post a reply in a thread.
Is it a server problem?
BTW, this post probably should have been posted in the Forum Suggestion area?