It is almost like Dampening off of sprouting seeds. I wonder if it is related.
How to prevent seedling damping off | UMN Extension
In my experience, fungus issues can infect and overcome a plant within days. The orchid probably could have used some extra Calcium while the new pseudobulb was growing. If you can determine the type of fungus that caused this, you might have a better idea when the infection began...whether before/during/after shipping.
Here is a good guideline to different diseases (and pests, too). Hope it helps.
https://www.staugorchidsociety.org/P...ySueBottom.pdf