Epoxies containing crystals prior to mixing and curing are a relatively infrequent occurrence. With two part systems, crystals may appear in Part A or less frequently, in Part B. It is most likely to occur upon exposure to relatively colder temperatures during shipping or while in storage. Due to crystallization, the viscosity of the epoxy could increase. Also, a clear epoxy can turn slightly cloudy.
Most of the time, crystallization is reversible by adding heat. Generally, 1-2 hours at 80-100C will result in the crystals dissolving and the system returning to its original state. If the crystals do not disappear after heating, it could well be that the epoxy was accidently contaminated. The best course of action in this case would be to discontinue using the system.
With one part heat curing systems, crystals may not be removable, and the epoxy should be disposed, according to instructions on the safety data sheet.