Yes. That is correct that D.Gray-man will be going on hiatus, but it is not because of health problems. I heard from the people in Onemanga that Katsura Hoshino is being sued for plagiarism. I am not completely sure, but a lot of those people are saying that is the case and that might be the reality. Apparently, some of the abilities of the half-akuma people are a little too similar to another person's manga. I really hope this gets taken care of soon, however, lawsuits can take a long time to get taken care of, and it is unknown if she will be allowed to even write any new chapters until this is taken care of. Hopefully, the case will be dropped and/or a settlement can be reached.
To be honest, I am a little worried that this lawsuit could even cause her to lose her job. Luckily for her, D.Gray-man is a very popular manga in both Japan and the West, so it is less likely for that to happen, but it is still a possibility. At the very least, it is not a health problem because if it was, I would be very worried about her overall condition. As I said before, hopefully the hiatus will not be too long.