Sad development indeed. If you can get a fecal done it helps with diagnosis. Sometimes pet stores cross contaminate by putting new animals in with other species increasing the chance for parisites. Some animals especially froglets fail to thrive and it’s difficult to determine a cause. Horned frogs produce thousands of eggs with the assumption that a few will survive. In capitivity all the natural pressures are lessened but there still can be developmental issues in the tadpole stage that manifest as unhealthy froglets. Best of luck.