Why one of Conqueror's torpedoes failed

Why did one of HMS Conqueror's torpedoes fail to sink an escort?

It apparently failed to detonate; the fact that the other aged Mark VIII torpedoes worked reflects their maintenance quality.

The simplest explanation for the nonfatal hit is that the torpedo failed to detonate. Conqueror was firing Second World War-era Mark VIII weapons decades after their original introduction. Two successful detonations from the salvo demonstrate that old equipment can remain effective when carefully maintained. The failed weapon is therefore both a reliability caution and a contrast with the technical skill that kept the others serviceable.