Greetings from a beginner, this is my first post. I just figured this one out: I also managed to test the parachute in descent, but after my ship fell below the required speed & height the test indicators went grey again, and the contract was not fulfilled upon landing.
On my third attempt on the launch pad, I realized that the parachute and the decoupler under the capsule were on the same stage. I added a stage, dragged the decoupler there, and after that the test went perfectly.
Clearly arming the parachute while decoupling was what ruined the test.