It looks like a moisture issue to me, especially on the second plant with the moldy soil. Container plants need excellent aeration at root level and the soil should be allowed to dry somewhat between watering. The ideal is to try to keep the soil just barely damp throughout, not overly wet and soggy but not allowed to dry out completely.
Goeppertia (formerly classified as Calathea) also like a lot of humidity which can be attained by sitting the pot atop a tray of moist pebbles and always keeping a very small amount of water in the pebble tray.
