Long standing issue with saving listings to wishlists in the APP, you can't save to an existing wishlist so you end up creating multiple lists with one listing each. To add "insult to injury" you then need to go in on a desktop to re-save to the list you want, and then delete bad lists.
This has been that way for a long time and I keep hoping they'll fix it, figured it was time to bring it up!
I am sorry to hear this and we appreciate you sharing your thoughts about it here. I'll make sure to pass on your feedback. it'd be great if you could let them know directly as well via the Feedback Form.