I had the same issue for years until i asked a knowledgeable friend to look at my seat height and position forward and aft. He suggested lowering my seat about 1 cm and that did the trick! I was so surprised and concluded that the problem is circulation from my middle. He suggested that there is a balance between a seat too low that hurts the knees or too high for toe and other issues. And it is an extremely fine line, at least for me. The other ideas in this post have good merit too, however, good luck!