On April 21, 2018 TPM reported, North Korea Says It Will Suspend Nuclear Missile Tests.
However back on October 13, 2017 CNBC warned the Latest North Korea earthquake was a sign of instability at nuclear test site after it's nuclear test blast on September 03, 2017
Then on October 31, 2017 Bloomberg was reporting 200 Died in North Korea Nuclear Test Site Accident.
After that report on November 01, 2017 a headline in Newsweek read, North Korean Soldiers Are Being Treated For Radiation Exposure After Nuclear Test.
Now of course we have no way of knowing if these reports are accurate. There's a lot of disinformation out there when it comes to North Korea. However if true it seems to me Kim Jong Un would have a huge incentive to bag future nuclear research. Especially when you think it's possible he could have lost most of his researchers, equipment and the millions of dollars it would take to replace them (if it's even possible). Course we don't know what he may still have laying around. This is still something we should be concerned with.
Trump, South Korea, China and Russia are all trying to take credit for Kim coming around. Maybe... just maybe these could be the real reasons. We may never know for certain since everyone seems to want to exploit this for their own political purposes (including Kim Jong Un).