Does the the undecidability of the Halting Problem eliminate the possibility of 'Hard AI'?
You're understanding of "solve all instances of the Halting Problem" is flawed. All instances means ALL instances. Every single one, ever.

For example, no human knows if a Turing Machine verifying the Collatz Conjecture will halt. Bam, right there, your premise that humans can solve "all" incarnations of the Halting problem is flawed.

There is no reason to think that a sufficiently good AI wouldn't be able to solve the same, or more, instances of the Halting Problem that humans can.

The undecidability of the Halting problem means that there is no algorithm which solves the halting problem. That means there is no algorithm Humans can use, and no algorithm machines can use. The proof doesn't rely on what the algorithm runs on.

Another way to look at it is that the halting problem, and other undecidable problems, essentially boil down to searching an infinite space. The inability of humans to time travel and examine an infinite number of instances doesn't negate our intelligence, so there's no reason it would for machines either.