There isn't necessarily anything wrong with the plant, and growing conditions like sunlight level (if getting more shade than it used to), soil moisture, and soil richness (if over-fertilized or growing in too much organic matter) can all impact how compact and sturdy-stemmed perennials can be. Crowding with neighboring plants might contribute to stem leaning, though we can't tell if that is the case here, though it is close to the lavender neighbor. In either case, the plant pictured looks healthy, and if it continues to flop as it matures, perhaps putting a support ring around the plant (as is done with peony) will help to keep it more upright.

Miri