Of course, when i say no reason i mean "apparently" no reason because nothing happened on the server (forced shutdowns, data corruption, deadlocks, etc...).
I ask this because, there was an application which executed a simple select on PostgreSQL:
select * from product where barcode = '9990000088355'
Which returned nothing, but there was a record in the table with
barcode = 9990000088355. There was an index specific for this field, and after reindexing it, the problem was solved and the query fetched the record.
So, is there a reason for this issue to happen, and can i do something to prevent this or at least see if there is a problem with other indices of another tables?