This was the second Soviet attempt at a robotic circumlunar mission as part of a larger project to send cosmonauts around the Moon.
On this launch, one of the four second stage engines of the Proton-K rocket failed to ignite at T+125.5 seconds due to a break in the engine nozzle. The wayward booster was then destroyed on command from the ground at T+129.9 seconds.
Once again, the emergency rescue system was activated, shooting the 7K-L1 descent module away from the rocket. The capsule landed by parachute about 50 miles (80 kilometers) southwest of the town of Dzhezkazgan.
The actual impact was a hard one because of a spurious command from the altimeter which fired the capsule’s soft-landing engines at an altitude of about 3 miles (4.5 kilometers) instead of a few feet (meters) above the ground.
Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.