Dendrobium nobile canes softening at the base

[Orchitty]

Hi. I love dendrobium nobiles and bought several last year during the Spring. They were outside under shade cloth where they got plenty of sunlight and watering about 1-2 times a week from me or the rains. Several of them eventually started to get soft (seemingly from the inside) at the base of the canes and then break off at this area. Anyone know what happened or what I did wrong? From what I've read, during the growing season, they are supposed to get lots of water. Did they get too much water? I've also read that nobiles tend to burn easily at the base of the canes? Is this what happened? I'd appreciate any info and advice from the experts. Thanks.