The best way to tell is to dig up the rhizome to see its condition. A healthy root system should be firm like a potato. Softy and gooey would indicate over watering (or freeze damage to outside plants)

In any case, more description of how they looked- leaf colors/spots, trunk appearance,etc. would be helpful.

The plant leaves slowly and evenly turned yellow until dead.

The rhizomes were soft but not mushy.

Could the problem be that I used regular potting soil.

Anyway, my care of the plants never changed over the three years.

I just don't get it. The plants were so robust and growing quite fast. Then one by one, gone.

I have quite a few varieties of house plant all doing well for years.