I had similar issue with missions "to repair a communotron 16 antenna on a satellite". One of them I have cancelled because I couldn't fiure out why it wasn't working. Another time it happened, I used the ALT+F12 (which I'm trying to avoid at any cost when possible) proposed by other players.
The two missions above, that I had consecutively, have one thing in common - the satellites were marked as DEBRIS, and before moving to the satelite I have changed it to another type(PROBE) for convenience to filter them on the map. I guess that when you change the type or the name of a spaceship it changes its identifier which is obviously different from what was initially in the contract.
I'm saying this because I managed to complete other contracts of this type, and in those cases I hadn't changed the type of the mission satellite.