I can relate to this too! Schatzie is like this. Only once in awhile do I notice it but she definitely gets an arch in her back quite often.
Im guessing it's a flaw in the breed - as Schatzie has many.
But....I just love her to pieces and realize I have just as many.
Im not sure to be honest about the "health issues". Im guessing she will have more issues with her LP (Legges Perthes) with arthritis setting in upon an older age, but that's ok, I will just carry her around where ever she needs to go and ease her pain as much as I can.
Here's a pic that really shows her "arch"....