A question arose (has arisen) regarding how the North Korea Rocket program moved from lousy into very very good. As you might (or might not) know the first great leap for North Korean rocekt design came after the end of the cold war and the dissolution of the Soviet Union.
After that happened, there were quite a few unemployed rocket scientists from the Soviet Union that ended up moving to North Korea. There was a surge of success, then a lot of failures.
Quietly, the United States (and China?) infiltrated the North Korean computer networks, and then there were a lot of mishaps, bad launches, explosions that were unexplained. And then, this last year, amazing success with North Korea's rockets.
After studying the pictures of the new successful rockets, intelligence officers found they were really similar (as in "the same") as Russian ICBMs. This was not tied to Russia.
Until Russia took Crimea from Ukraine. Ukraine / Russian trade and cooperation went right into the pooper.
Which leaves the Ukrainian missile factories and their rocket scientists without employment. Now they turn up in North Korea too and the rocket technology has increased by leaps and bounds, far outpacing our estimates.
Why would Ukraine do this? Probably the number 1 reason is money. Ukraine is pretty damn poor after the Russian attacks. Now, it is technically illegal, but so was attacking the Ukrainian territory and no one seemed to care. Their territorial integrity was guaranteed by the US, Russia, France and England, which lead to Ukraine giving up their nuclear weapons. As it turns out, big ass mistake.
We all sat by as Russia took the Crimea and then started hacking pieces off Eastern Ukraine.
The upshot of that is that, yep - Ukrainian scientists have helped North Korea jump start their ICBM production.
Of course, I wouldn't be fair if I didn't point out Ukraine denies all this. They say Russia is helping North Korea and trying to smear Ukraine's reputation. There is more than a little possible validity to this, and the evidence could point either way. But more towards Ukraine (link).