My track doesn't appear. Why?

I’m new to OSM but I already managed it to log some tracks with my Garmin GPS Logger, edit these by JOSM and upload them to the OSM server.
Some of these tracks appear on OSM (Mapnik and Osmarender) and some of them only appear on Osmarender in the highest resolution zoom, even a few days after uploading the data.
When I download the data from the OSM database to JOSM these tracks appear.
Where’s the problem and what could I do to fix this?

Thanks.

Well, as you say, all your tracks do appear in Osmarender so that’s how you can tell it’s not an mapping problem if this happens again.

More info here: http://forum.openstreetmap.org/viewtopic.php?id=3271