Hi @zoomdeathknight I'm definitely not the authority on this, and please feel free to go research it yourself, but from my knowledge:
She's posted several transphobic tweets (over the last few years) and proudly views herself as a "TERF" (trans-exclusionary radical feminist). Due to her position as a well-known and influential figure, this is very harmful to the trans community.
I believe some people also pointed out heavy links between the goblins in the hp series and Jewish stereotyping, as well as other things like there being very few non-white characters across the series.
There are also other things, like when she essentially said 'oh Dumbledore's gay and he always has been' and then didn't do anything about that even while the first couple of fantastic beasts movies were being produced. Personally I found the second one quite annoying in that respect, (with the blood promise or whatever it was between him and Grindelwald) and just a bit rubbish anyway. I watched it before I knew about all the above and I didn't bother watching the third