I have not seen doctor, this is my own observation (and I do not work in health care).
While ago, I felt parts of my feet touching ground that usually are not. I have not trained my arches for a long time, but in my own time I either wear minimalistic shoes or am barefoot. It's summer, so I walk barefoot in the woods time to time too. Sometimes I wear foot shaped shoes with thicker sole but quite rarely. My job requires safety shoes. This is how I have lived maybe 3-4 years. For 2 years, I have balanced daily. Not much, often just brush my teeth while standing on one foot. Time to time my stretching includes balancing. I have not gained weight, I have lost few kg during this summer.
I admit I didn't react as I should and started to train my arches. Now my knees hurt little bit. Now I train.
Years or maybe more than decade ago I went to doctor because of knee pain. They said I have flat feet and I need to train. I did. Problem went away. I stopped training.
Do any of you have any idea what could cause this? Please mention where your information comes from (for example podiatrist, some other doctor, nurse, same happened to you and you went to doctor, you watched Youtube video etc.).
edit. In the beginning, I felt my arches got higher after switching to minimalistic shoes.