'missing' data on replicate

I have 4 machines in a cluster: 1 master & 2 replicates (hot standby mode) on OSX, 1 replicate (hot standby mode) on Linux (centos6.5). All replicates were created with pg_basebackup (+ X option).

I have a table that returns no results when queried by the primary key on the replicate running on Linux. The same query returns data on all other machines in the cluster. The data is there, if I query on anything other than the PK, I get the results I expect.

a) Is this a corrupt index? Something entirely different?
b) How can I rebuild index on slave? Rebuilding on master did not fix.
c) What are the possible ways of getting this way?

I’ve never seen this before and I’m not really sure how to proceed. I can take the Linux machine offline and rebuild the whole thing but I would rather know how this happened & fix it in place. We are in the process of migrating everything to Linux and this box is a test bed. Before I commit everything to a new linux cluster I’ld like to understand what I am seeing.

thanks
alan