I wonder if you're getting close enough to the plants that you photograph with the app, Barmaid. You really need to get in close to get decent results from it.
I was at Green Island Gardens
https://www.greenislandgardens.co.uk/
with a friend last Friday. She really knows her plants, having lectured in horticulture and run a garden design business. She can usually rattle off the Latin name of any plant, along with numerous common names for it, easily. However there was just one plant that stumped her last week. I used the LeafSnap app to try to identify it but my friend cast doubts upon its primary suggestion. Later, however, she asked the owner of the gardens about it and she confirmed that LeafSnap had actually got it right.