I have almost the exact same problem. We discovered recently that even though our son is still on our health plan, he is no longer our dependent. So we asked our HSA bank if we can return the 2019 funds with a mistaken distribution form and get a corrected 1099. We did, but now they say they can't correct the 1099. And that our mistaken distribution that we returned will show up on our 2020 1099. I am still a bit in the dark about how I fill out our 2019 taxes because of this.
