Welcome to summer lol, our lab is a tick magnet and we use advantix2 as well and got real frustrated as he would always come out of the woods with ticks on him, contacted our vet and got the whole story then felt better. The advantix has permethrin to help repel ticks, as you know not real good at times, the real job that advantix does is kill the tick and it falls off, mind you this takes from 24 - 48 hours. This is why we find ticks shortly after coming in from a romp, the tick has not absorbed enough product nor has enough time lapsed to cause the death of the tick.
Our vet assured us it works, but to keep checking him and removing as we had been, but the advantix will get the ones we miss. I will say we have found dead ticks on the floor so I know we have missed some, and also that the product works as it is indicated.
It is frustrating as all get out, but I believe it is the proper way to treat the issue.