Second sunset platy dies after three months

A pair of sunset platys had been purchased in September 2017, One of the sunset platys died soon afterwards while the second one survived.
However in december 2017, the second sunset platy was also found floating at the top of the water in the fish bowl due to unknown reasons
After some time, the fish had disappeared and the water will have to be cleaned.
The sunset platy was kept with goldfish, which continue to survive
So clearly platys, especially sunset platys are not very tough fish, suitable for living in fish bowl,as they die quickly