I started a brand new game one or two releases ago (actual build is 73 if I am not mistaken). After I went to the moons, I found a Titan wreckage on both of them. The first Titan was in the midst of the Zirax base, while the second was on a much calmer moon with Polaris mining outposts.

In an attempt to find the engineer's lost key card, I used a salvage core and located a suspicious-looking "engineer's bed", so I knew it was there. I went to pick it up, but nothing happened (I expected to find it in the nearby locker). Knowing where to look and having two Titans on my disposal, I went to the other one (on the Polaris moon) and was able to get the key card from there (unsurprisingly).

However, when I wanted to use it on the twin Titan wreckage on Polaris, it said "Can't interact with the NPC in a player based structure" something. Then, I fought my back way to the original Titan (at the Zirax base), killed the anti-air towers, massacred ~1000 Zirax troopers, only to see the same message - no NPC interaction in a player based structure.

Now, I might have used the damn salvage core in the second Titan as well (I can't recall at this point), but that is a serious issue anyway. The Titan should have been protected, only to allow salvaging once you finish the quest. That way, no salvage cores could be (mis)used. Also, dual Titan should be fixed somehow, although I haven't tried to reproduce the issue starting yet another game.