This may be a sign that Uncle Jang was in fact purged in North Korea:
The Rason Special Economic Zone, which was headed by Jang Song-thaek, the once-powerful uncle of North Korean leader Kim Jong-un, has been left as a ghost town after Jang’s purge, and several North Korean officials who worked in the zone are under questioning, a source in China said.
“On Nov. 3 to 4, I visited the Rason economic district,” the source exclusively told the JoongAng Ilbo, “but I couldn’t meet with the two main officials in charge of the zone’s development because they were both sent to Pyongyang.
“The two officials were in the inner circle of Jang Song-thaek and they were in charge of developing economic zones of North Korea,” the source said. (……….)
With the purge of Jang, most of the Chinese officials have left the zone, and the North Korean officials are scheduled to return to Pyongyang soon. All activities at three piers in Rason’s port have stopped with the downfall of Jang. The first pier, run by a Dalian-based Chinese company, suspended its transportation of coal, and the construction of a second pier has been halted. The construction of a third pier by a Russian builder was also suspended. [Joong Ang Ilbo]
You can read more at the link, but one of my working theories has been that the North Korean military saw the economic projects Jang was promoting with China as a threat to their power base and thus maneuvered to strip Jang of his power.