Apt-Get upgrade finds the US repository unready

Two days in a row, when I ran sudo apt-get update and then sudo apt-get upgrade, the console said that there are upgrades ready to be downloaded, but when I ask for them, it turns out that the files aren't there yet.

This applies to the US repository. Not sure about any others.

Details:

> Need to get 321 kB of archives.
> After this operation, 0 B of additional disk space will be used.
> Do you want to continue? [Y/n] y
> Err http://us.archive.trisquel.info/trisquel/ belenos-security/main libspice-server1 amd64 0.12.4-0nocelt2ubuntu1.1
404 Not Found [IP: 208.118.235.52 80]
> Err http://us.archive.trisquel.info/trisquel/ belenos-updates/main libspice-server1 amd64 0.12.4-0nocelt2ubuntu1.1
404 Not Found [IP: 208.118.235.52 80]
> E: Failed to fetch http://us.archive.trisquel.info/trisquel/pool/main/s/spice/libspice-server1_0.12.4-0nocelt2ubuntu1.1_amd64.deb 404 Not Found [IP: 208.118.235.52 80]
> E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

What was there at the time:
> libspice-server1_0.12.4-0nocelt2ubuntu1_amd64.deb 08-May-2015 21:18 320750

What was not there:
> libspice-server1_0.12.4-0nocelt2ubuntu1.1_amd64.deb

What showed up a little later:
> libspice-server1_0.12.4-0nocelt2ubuntu1.1_amd64.deb 08-Sep-2015 14:04 321176

Same thing happened again today ... admittedly the delay was only a few minutes, but it's disconcerting to hit the server at the wrong moment two days in a row.

Shouldn't the files actually be present on the server before letting the server respond positively to an upgrade request ?