If it isn't seen in the receiver, you might suspect problems with the receiver, the antenna, or the spacecraft. The computers of the telemetry system make sense of the radio symbols modulated onto Cassini's downlink. They turn these radio symbols into the ones and zeros familiar to computers everywhere, then pass them along to JPL via the communications system. If you've ever set up a modem and configured your computer to talk to a data service, you know that data communications are not always one hundred percent easy and reliable. Configurations can be set incorrectly.
Circuits can overload.
Severe weather, as well as solar flares, can interfere. Land lines can fail. Once received at JPL, there are more telemetry system components that process the data. There's an interface with the communications link. Then, there's the storage and distribution of the data.