How to figure out why there's a warning triangle?

[psykix 97]

I have several albums with warning triangles. They have cover art, they are identified and have a musicbrainz id which when clicked takes me to the correct album on Musicbrainz. The artists is recognised.

 

So how do I find out what the problem is to eliminate the triangles?

 

It would be great if the warning triangle would give you a bit more of an indication of what the issue is.

 

This is one example :-