Hi Felipe,
My first guess is that you have content entitlement enabled for this partner.
What does:
mysql> select * from category_entry where entry_id='0_4jeh0s9v';
return?
If indeed, content entitlement is enabled, you can set:
$privileges = "disableentitlement"
when generating a KS and then make the same request.
This is what KMC does, thus bypassing the entitlement mechanism.
If that does not help, first check in KMC whether you see this entry attached to the category in question, if you do, obviously it is not a Sphinx issue, if you don’t see it attached to the category in question in KMC, make the request again and check the queries that go to both MySQL and Sphinx in /opt/kaltura/log/kaltura_api_v3.log and let’s see where it goes wrong…