Certified GKH Gardening Expert
The MiracleGro will be the cause here. Anything with slow release, or too much nitrogen will prevent flowering. You will need to switch out the soil with something that does not have a slow release nitrogen, but higher amounts of phosphorus and potassium.
This article will help on the care of these: https://www.gardeningknowhow.com/ornamental/flowers/fuchsia/growing-fuchsia-flower.htm