I have 2 large plants in pots, which have been fine for about 3 years and this year have shown that the flowers were about to open, but suddenly both bushes have shed many leaves and the flowers are drying up and falling off. Would they revive if planted in the ground, or could ants have got into the pots and caused this damage?
These are fast growing plants and they may have outgrown your containers.
They also will not tolerate wet roots and can die from root rot very quickly.
Check the soil.
Certainly pests or disease are also a possibility, so inspect the plant and soil for signs.
I do think this shrub would be best planted out into the ground.