HH -I have a white variety which has flowered constantly since it was bought last year for filling holes in a sandstone wall in last house. I had 1 left over so it's come with me to new house and has flowered all winter in its container. They're really like aubretias - mine were in a very exposed spot but had good drainage as they were in the wall, and I just trim old flowers off. Has it maybe got a bit waterlogged in the middle? Some might be more fragile than others but if it's growing now it's probably fine.
I have hard pruned them before with good results. I have a pink one hanging over the edge of a planter which looked so pretty last year that I couldn't bring myself to prune it and now it's flowering near the compost and at the end but there is a big brown patch in the middle. When it's finished flowering I shall cut off all the overhanging bit.