My current WIP is a YA book that I've plotted out to be a trilogy. The first book is written (and revised) and comes in at 56k words, with parts two & three expected to be around the same length. As I intended this to play out over three books, I've left certain plot points partly unresolved with a view to them becoming the focus of the subsequent books. Would ending like this be off-putting to agents? I'm just about ready to start querying.
Most series writers, certainly those I've read, leave certain issues unresolved. I don't think that's a problem.
Where it can be is if you leave the main thrust of the story hanging in mid-air. That sort of thing can leave a reader feeling short-changed, not recommended when you want them to be intrigued enough by the thought of what might follow to buy the next book.
As long as the main story in this part ends, happily or otherwise, you should be fine, I'd have thought.