Certified GKH Gardening Expert
Most miracle grow products contain slow release nitrogen, and quite a bit of quick release nitrogen. This will halt flowering. This would be my first guess. You will have to offset this with potassium and phosphorus, or by raising the pH just slightly.
This article will give you more information: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/hibiscus-fertilizing.htm
This article will help you to grow Hibiscus properly: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm