You are not alone. 
I pushed some burr comb wax into my Flow frames, and my hive started using them within a couple of days. However, my hive has 2 brood boxes and was very strong when I put the super on top. There is a very helpful thread with lots of ideas, linked below, but I think the most likely thing is just that some bees take their time. Once they start using the super though, they will use it much faster the next time. Several people have had to wait 2 years to see the bees use the frames, then after the first harvest, the bees refill the super in 2 weeks. Just one of those unpredictable things. 