There are so many reasons a plant might decline to bloom, I can't diagnose it from the information you provide.
High nitrogen would probably not stop blooming, though it tends to
promote extra-lush foliage. However, mint compost is not overly high in
N. It does have potassium salts, which could be accumulating - it is
generally better to rotate different mulches over the years.
The buds could have been destroyed by an untimely freeze - this happened to a lot of plants this spring.
Does the plant look healthy? Are there any signs of disease or insects? Do the leaves look odd in any way - chlorotic, discolored, etc? Were there any flowers at all? It may be too late to tell, but did it form buds which died, or no buds? Is it forming buds for next year (azaleas and Rhododendrons bloom on the previous year's wood, so they are doing that now).
Have there been any sudden changes to its growing conditions - more or less water, excess water in winter, a tree removed so it is getting more sun, root damage from construction, etc...
If you answer those questions as well as you can, and provide pictures, I may be able to help.