What is the ideal way to store canning?
In a cool dry place around 10C out of direct sunlight or bright lights. Lights will cause foods to fade in colour and loose nutrition, e.g. relishes

What causes a jar to lose its seal (the jars seals and then unseals)?
Food particles might be on the rim of the jar, tiny chip in jar rim, under-processing the filled jar. Excess air may have been left in the jar because of too much headspace or air bubbles many not have been removed before processing.

Why do the undersides of metal lids sometimes discolour or have black spots?
Natural compounds in some foods, particularly acids, corrode metal and make a dark deposit. The deposit is harmless and does not mean the food is unsafe to eat, e.g. pickled asparagus or pickled eggs.

What makes pickles go soft?
The ratio of salt/ vinegar brine is not correct ratio. The vegetables are too many days old. (Optimum quality for cucumbers is 2 days fresh) The canning temperature is too high.

Why is there mold on top of some pickles after opening?
Even when properly processed and refrigerated after opening pickles are susceptible to mold, especially any vegetables sticking out of the brine because they are exposed to air, e.g. dill pickles or pickled carrots.