It could be a medical condition entirely unrelated to their mission. If it's unrelated, the astronaut deserves their privacy. If spaceflight made their condition worse in some unexpected way, that should probably be made public. Maybe NASA is just waiting to confirm which option it is?
I feel a medical event that happened during a mission should be worth reporting even if it doesn't seem related at the time. There are so few humans that have spent significant time in space, less than 1000 that have went for any time all, and nearly all of them have been publicly funded research missions. Rather than hide data that seems innocuous at the time we should be gathering and sharing that until it's not such a rare research oriented project to travel to space. If you can't put your personal medical privacy interests aside then you shouldn't be the one signing up and being selected for such a public research service function.
At the same time I imagine this issue is something extremely mundane... which makes the lack of transparency and resulting media stir even more grating.
