Hello, I had similar symptoms If somebody else is using machine it happens to be bend/ squeezed too much bobbin case that it starts to jam or some new bought bobbins from different manufacture (or some dents and bends on it's wall if it is not new) sometimes can fit too tight not only in diameter, but height of bobbin also is important and even harder to spot that something is wrong. I am trying to keep thread away from oil because it can change colour but i use silicon oil spray for thread and needle if sewing through the sticky glue. Love to watch You working and creating shoes❤
