Can't play or download matched songs

I have uploaded my entire library via Match and moved all my music off to an external HDD but some tracks will not play when signed in to Match.

The tracks have the cloud icon with the download arrow next to them but when I try to play or download them absolutely nothing happens.

This is the case with a large number of songs including very mainstream stuff that is definitely on the store.

What's going on? Why can't I play them or download them even?

Thanks