The first credible report that something was wrong with Kim Jong Un came from Daily NK that said he underwent a "cardiovascular surgical procedure" the previous week and was now mostly recovered. Hours later, CNN report suggested he was in "grave danger" after surgery. Other theories include that he might be in self-quarantine or got injured in a military drill.

from Times of India https://timesofindia.indiatimes.com/world/rest-of-world/top-theories-on-whats-going-on-with-north-koreas-kim-jong-un/articleshow/75419566.cms