[Ben Hecks]

"A disease course that the doctors haven't gotten a full story on, so it's
a challenge for them to solve"

Since this soldier was assigned to an Engineer Battalion, he may have been involved in grading or other earth moving operations that stirred up a lot of dust. If so, he may have contracted something similar to Valley Fever which is sometimes fatal.

[Domestic Church]

"... he may have been involved in grading or other earth moving operations that stirred up a lot of dust."

You probably hit the nail on the head.