Fremont was very slow (Internet, not servers) for a while (until now). Something happen(ed)?

the internet is like a series of tubes...

Yes but when everything is working ok but Fremont access (slow), the tube is identified isn't it?

probably the fastest way to get help is to jump on linode's channel on irc, or to get an official response you'll need to submit a ticket.
but you'll need an mtr in both directions. you'll get asked for an mtr in both directions, so do it first, and provide it when you ask on irc or submit a ticket.