Your screenshot shows a calligraphic brush clearly selected in the Control Bar. It also states "5 pt. Round" in the Control Bar. "Uniform" refers to the stroke width profile, but brushes have some dynamic abilities in addition to any width profiles.
To remove the brush dynamics which are most likely the reason your stroke widths are varying.... Click where it reads .'5pt Round.. and then click the Basic option (which means "basic path, remove brush strokes").
This should result in a standard stroke path with a uniform width along it.
If you wish to draw freehand but not use brush dynamics, you need to be certain to click "Basic" for your brush paths after they are drawn... or use the Pencil or Freeform Pen tools rather than a brush.