Why did bombs hitting warships fail to explode?

Why were bombs hitting warships failing to explode when the type was normally reasonably reliable?

Arming errors or releases too low for the fuzes to arm are proposed explanations. Higher-flying flare aircraft had better results against fuel installations, but the cause is not established.

The 250-pound bombs had a reputation for reasonable reliability, making the failures against warships difficult to explain. One proposed cause is a mistake in arming them. Another is that aircraft staying beneath the barrage dropped their bombs before the arming mechanism had enough falling distance to complete its movement. The comparison with low bomb releases in the Falklands war illustrates the same problem. Charles Lamb and other higher-flying flare aircraft achieved better results against fuel installations, which is consistent with the release-height explanation.