The Discover Magazine article How New Horizons Survived the 40-Year-Glitch and Made it to Pluto is a little confusing. It wraps NASA history together with several different space missions to get the "40-year" value, since New Horizons was launched only about eleven years ago.
The engineers have become so good at fixing problems that most of the time the public has no idea what they are up against—until something goes wrong, as happened to New Horizons last weekend, when a software glitch caused the probe to shut down into “safe” mode. For a moment, this was a news story. Then, once again, the engineers stepped up and solved the problem (caused by an obscure timing flaw in a command sequence sent to the probe in preparation for flyby). Within three days, all was back to normal.
In the linked NASA News item NASA’s New Horizons Plans July 7 Return to Normal Science Operations, the issue is also mentioned:
The investigation into the anomaly that caused New Horizons to enter “safe mode” on July 4 has concluded that no hardware or software fault occurred on the spacecraft. The underlying cause of the incident was a hard-to-detect timing flaw in the spacecraft command sequence that occurred during an operation to prepare for the close flyby. No similar operations are planned for the remainder of the Pluto encounter.
Q: Is the glitch described in any more detail anywhere? Was it purely a software/computing timing issue or did the timing involve comms or something mechanical as well?