Depressor labii inferioris weakness
This is caused by weakness in the DLI on the right. Often this is seen when the marginal mandibular nerve is injured. This can be a congenital problem, but mostly related to prior trauma or surgery around the jawline on the right side. If it has been there for years, it won't get better. Some docs recommend placing Botox in the opposite side to make symmetric but this can affect the way you manage food in your mouth and it can get stuck in front of your lower teeth.