Common causes of jars breaking during canning process

Q. Why do jars break during processing?
A. Jars break during processing for the following reasons:
• Canner became dry during the processing period. This is caused by either a steam leakage in your canner, which means you need a new part, or by using insufficient water for the processing period.
• Commercial jars (pickles, spaghetti sauce, etc.) were used instead of the recommended glass home canning jars.
• Cracked or nicked jars were used.
• Food was packed too solidly or jars were overfilled.
• Lids were overtightened (follow lid manufacturer’s directions).
• Cold jars were immersed in boiling hot water. Food and jars should be hot when placed in the canner.
• Jars were placed directly on canner bottom. A canning rack should always be placed on the canner bottom. It is not necessary to place a rack between a layer of pint or half-pint jars. Stagger the jars by placing a top jar on two bottom jars (see picture).
• Pressure was reduced quickly after processing. Always let pressure drop of its own accord.
• Air was exhausted from canner at too high a temperature. Adjust heat so a steady gentle flow of steam emerges from the vent pipe.
• Pressure had fluctuated during the processing period. This can be caused by an unsteady heat source or steam leaking from the canner.
• Jars were placed in a cold, drafty place to cool. Cool jars on a towel or rack at room temperature.
• The jars themselves are very often the cause of difficulty. They eventually weaken with age and repeated use.

Ref:  https://www.gopresto.com/recipes/canning/faq.php