Hi!
So I saw a few guides on the forums for this questline, and I made sure to have a pokemon with Foresight on me when I entered Alucard Castle. I then went to the trash and saw the hint, following that I went to defeat all the ghosts in the place, I've triple combed the area to make sure I missed 0 ghosts. I then progressed past the old men and up to Alucard, I've battled him about 8 times now, each time I've won except a few times where I've forced a loss for myself to see if it would trigger what was supposed to happen.
As you can guess, it didn't trigger anything at all. Maybe I'm missing something but I asked on the discord Support channel and was told to make a bug thread on it :)
Thanks for the help!