Anyone who has worked with or as part of a team recognizes that often skills may seem unrelated among team members, yet they come together to complement each other and make that team function.
The question might not be "What were they working on and how is it related?" so much as "If I put these people together on a team, what could they do?"
I worked on an Archaeological crew, and we had people who ranged from Archaeologists and Geologists to people whose areas of specialization were history, art, photography, music, and even a couple who were cooks. The list, presented at random, might not have seemed to the untrained eye to be exactly what you'd be looking for to do Archaeology, but as a group, the team was very effective at finding sites, excavating and documenting them, etc.
So the question is not necessarily one of what did these people do, but what could they have conceivably done as a team or working in concert?
Of course, multiple frameworks could be overlaid, which might confuse the attempt to find a pattern, too, but the skew seems to be toward the types of people who could build (or reverse engineer) advanced spacecraft, with currently unknown propulsion systems, with AI navigation and/or control.
That is just one possibility, and these disappearances may not necessarily have a sinister aspect so much as an absolute lid for security purposes (where no one not directly involved would even know where they are or what they are doing, provided they are still alive).
And at the bottom of it all (as unlikely as it may seem) those who have been reported dead, may just be so, and it may be coincidental.
Strange circumstances of disappearances and having access to highly classified research in common makes fertile ground for theories that would be based on anything but coincidence.
