Hub, problem comes from OVH, they are very unreliable with Piwik hosting on their “Mutualise” servers… see for example 301 Moved Permanently and many other posts
OK, that may be. I was assigning the blame to Piwik, as it “used to work perfectly” with previous versions.
The problems started appearing mid-january, when I upgraded to 1.6. Then again, I hadn’t gone querying the 1.5 stats for a while, so it may have been broken before the upgrade.
FWIW, I’m using the same database as before (new tables), hosted on the same SQL server.
It may be that newer versions are exercising the mutualized machines in ways that are constrained at OVH.
I may try reverting to 1.5, just to see what happens…
Its definitely a OVH problem so please ask their support
[quote=matt]
Its definitely a OVH problem so please ask their support[/quote]
That may be, and I will definitely try to open a ticket with them.
But… I’m willing to bet they’ll claim it’s a Piwik problem. Assigning blame is easier than actual debugging. 
In the meantime, I HAVE reinstalled a pre-1.6 version (I believe it’s a 1.5, dated August, 2009).
… and, that version does work at OVH.