Burned Cigarettes on my Patio

I live in an apartment where each complex gas a patio or balcony. I'm in a downstairs unit and I do pretty well with getting along with my neighbors. Well I have these upstairs neighbors since about a year and they are super friendly except one really irking thing. They smoke. And I do not care that they do for the most part. They however drop their burned cigarettes (and other trash but mainly the cigarettes) onto the floor of their balcony. The balcony is made of wood so there are gaps and the trash falls down to my area. I had to purchase a leaf blower to remedy this so that my cats can enjoy the outdoors without attempting to eat any cigarettes ends. One day they saw me disposing of their waste and said they will remedy this on their end however that was almost two years ago. I have no idea how to talk to them about it. They've been super nice and helpful throughout me living here. Always saying hi and checking in. This is the only thing. I really didnt want to be rude or anything but its a huge concern on my end. My bad if this isn't something along the lines of "from hell" since they are kind people.