I have a host which is showing as online in the Kolide Fleet UI but any query against that host just keeps running without returning any results. Any suggestions of where I can start to investigate the issue?

Can you query other online hosts as expected?

yes

You are sure that this particular host should return data for the query? (Use something like this to be sure:

SELECT * FROM osquery_info;

)

yes

I would take a look at osqueryd on the host.