I bought four beautiful hanging ivy plants in March of 2018, and they all did well until suddenly maybe four months ago they all started dying slowly and at the same time with leaves turning light brown then dying. It's almost as though they were programmed to die. I can't find any rationale - no visible mites or other bugs. Has anyone had the same experience or can speculate on the reason?

It is hard to speculate without seeing the plants or knowing what kind they are (were?). It might be a watering issue.