The ascent engine failed. The rescue did not. That distinction is the program's defining one.
The LLS-2 ascent failure was the closest the MSC program has come to losing a crew. During the Mun ascent phase, the ascent engine on the lander stage underperformed, leaving the crew unable to achieve Mun orbit. Three kerbals were on the surface of the Mun with a vehicle that could not bring them home. Mission control declared a contingency. The program's Zero Crew Lost constraint - the line nobody crosses - was in jeopardy for the first time.
RETRIEVAL was assembled and launched within the contingency window. The rescue vehicle - using a proven L-SLS3+ stack - reached Mun orbit, rendezvoused with the stranded crew's ascent stage (which had achieved a suborbital trajectory on residual thrust), and recovered all three kerbals. The return to Kerbin was nominal. All crew survived. Zero crew lost held.
The Herald pressed NASA on the ascent engine anomaly. Administrator Clane confirmed the failure mode, confirmed the corrective actions, and declined to identify the crew by name in the public statement, citing medical privacy. The crew has since returned to active rotation. The Herald notes: this is the mission the program will be remembered for. Not the landing. The rescue.