MBB 20170520a
Concert theme: Ardent celebration for the Hwasong-12 missile 화성-12형 열렬히축하
Place: Mokran House
Audience: Military and technicians related with the successful test launch of the Hwasong (火星 Fire Star) -12 solid fuel intermediate range ballistic missile in 14 May. It rose to the height of 2,111.5km, flying the horizontal distance of 787km, and landing in the Sea of Japan. This would translate to an operational range of 3700 – 6000 km. Both domestically and internationally the test was considered a major success in the various simultaneously ongoing North Korean missile programmes
KJU: Not present
News video: https://youtu.be/Qcq4MoCFoSs
A high resolution photo: http://news.6park.com/newspark/index.phpapp=news&act=view&nid=236431

Comment:  The news in KCNA on the role of MBB in 20 May was simply: “At the banquet, there was an art performance of the Moranbong Band in congratulation of the developers.” (조선로동당 중앙위원회에서 지상대지상중장거리전략탄도로케트 《화성-12》형개발자들을 위한 축하연회 마련 //// Developers of Rocket Hwasong-12 Feted).
It is not known how long the concert was. It has not been published. Lyrics of two songs were shown in the two photos published of the concert in the news video:

1. 우리의 김정운동지 Uriye Kim Jŏng-un tongji Our Comrade Kim Jong-un (2015)
2. 사회주의 오직 한길로 Sahwijuye ojik hangillo Socialism is the Only Way,
a new song published first time in February 2017

MBB 20170520 leikattu

In the photo (non-essential elements cut out by me) it looks like the ensemble consisted of the original arrangement of instruments. Whether also the players were original cannot be told for sure, but the general shapes of at least violin players look like that. Sonu Hyang-hui is likely to be at the extreme left in her usual place. Also the saxophone is back. There appeared to be only 5 singers.

Why was the concert not published? Some possibilities:
1. It was too short? Only 2 – a few songs?
2. There is some kind of strong ban on Sonu? Also the concert in honour of visiting Cuban diplomats in 2015.09.07, where she previously appeared on stage, was never published.
3. Different sections of the propaganda machinery cannot agree on a common policy line, and MBB is administered by an organization that is weak at the moment?
4. The international diplomatic situation, where there exist both strong military posturing and careful diplomatic feelers about possible negotiations, does not favour celebrating a missile launch too joyfully?

No one knows.