I have had intermittent issues with my Turnigy 9x. I'm not sure to what every instance can be attributed. But, I have found one recurring issue. That issue lies with the receivers. EVERY receiver that I own has suffered a broken antenna. Most often this occurs at the point where the antenna wire leaves the RX casing. I have resoldered EVERY receiver that I own, only to have this occur again. Usually, I am unaware of the break until the next crash.
Also, wireless networks operate on 2.4 Ghz. These may interfere with the communication between the TX and RX. Another issue to be aware of is brown out. The voltage to the esc can momentarily drop, causing a reset of the esc. Within this moment, a crash can easily occur. A universal battery elimination circuit (UBEC) can help prevent this. Many esc's have an onboard UBEC, but an equal number do not.
I think the tell tale sign of a UBEC is a couple of capacitors hanging off the end of the esc. But, I could be wrong. You can buy stand-alone UBECs that act as a failsafe to any esc.
Good luck!