Yes, it certainly can be caused by a defective primer or one that has been compromised for example someone using WD-40 on their weapons since it is a penetrating oil. Not a good gun lubricant.
But in other cases it can be caused by a short powder drop charge or in some instances no powder at all and the primer ignition drives the bullet into the barrel of the pistol.
The main thing is pay attention to your pistols and if something seems, feels or sounds different "Stop Shooting" until you check it out! Squibs can happen!
The Constitution is not an instrument for the Government to restrain the people. It is an instrument for the people to restrain the Government!
Today, we need a nation of Minutemen, citizens who are not only prepared to take arms, but citizens who regard the preservation of freedom as the basic purpose of their daily life and who are willing to consciously work and sacrifice for that freedom."
-- John F. Kennedy