Strange I never had it since they fixed the problem. Well I guess that the server is still a little overloaded at some moments, probably not when I use the site myself, explaining why I haven't seen it.

Do you have that only with admin pages ? Or also on normal public pages ?

I think I'll switch to the other database server that I mentioned, for the little extra cost it should be much faster and solve these problems for a long time.
I'll do that on next weekend.