Command block not giving comparator output

I've been building a command block machine, but it turns out that one of the command blocks has stopped working. The rest give proper output when I step in the correct location. In image 1, it shows the faulty block, in image 2, it shows the command used (see image 1 for co-ord reference), in image 3, it shows where the faulty command block is placed and in image 4, it shows an example of a working block (the fourth one). Only the middle one does not work, the other four do.