Oooh, I like this! Connection on Newt's part had to be broken quite badly if he hadn't felt much when meeting Graves. I wonder how their next meeting will look like?
The idea with potion was great and the story you created around it is even better. It would suit younger Dumbledore to drink that potion after his sister died, and I'm not surprised Grindelwald waited so long - maybe he wished for Dumbledore to join him in the next?

I know it's greedy of me, but I can't wait for the next part!