If for example we are searching for a service like a flight and see that certain service is being offered by Galileo instead of Amadeus, this is normally because our system uses an algorithm to avoid showing that flight several times (one per each provider) and will only show that flight with the cheaper provider. This applies for any kind of service (hotels, tickets, transfers etc)
It can also be cause by availability timeouts. The system has a general timeout of 35 seconds and if the provider takse longer to give availability if will be discarted from the results