When investigating this we found a related issue. VGPS jobs with lots of unknown caches and "refresh corrected" never finished.
After we fixed the above bug, it seems like it's possible to download GPX files again. I can't personally see why this is related in itself, but since the download seems to work there isn't much more we can do.
Your already ordered file will probably not start to work again. But ask Project-GC to build a new one and that one should work. If it doesn't, please get back to us.
Sorry for inconveniences caused.