I had until last week updated the exact same issue. At end of the day always around 2000 steps different from the cellphone step counting, and no floor counting at all. After the update guess what? Now the watch is counting steps on its own! I woke up today and the watch was already with 2250 steps! Yesterday I got an alert of exercise in the watch like I was doing some running, but I was working sitting in front of a computer... Samsung does what's? Nothing...
he he! Its ridiculous isnt it! But hey did you see the announcement that they are releasing a new UI for all of the Samsung watched with much improved functionality apparently! Although they have said it will take a while to roll out but hopefully not too long! Lets see if that makes any difference at all. I will let you know if I get an update.
Remember, get to the top of the stairs and raise an arm above your head. You will look stupid, but it will register a floor. I'm surprised Samsung haven't included this advice in their instructions as they have no intention of fixing this age old problem.