The OP probably inadvertently double-clicked the vertical bar while trying to scroll. Double-click again as Cornico advised, so you'll get tracks back to the default simultaneously. Btw., I don't think VPro 13 "loses" that bar the way that MSPs 13 and 14 do. The + and - signs at the lower right corner allow you to adjust track heights as well. Richard's suggestion restores one track's height, as he says.