In Vegas Pro 17 the track number indicator (see red arrow in screenshot) is just showing track numbers and not showing the controls for mute and solo and volume and other controls. When I try to expand it horizontally there is no response... it just stays stuck.
First try hovering your mouse over the small gap between the track number part and the timeline to see the two-headed arrow button. Try double-clicking on it to see the missing track list. Then try clicking the hamburger (3 horizontal lines) button to be able to "Edit Visible Button Set".
And you can expand the track list as jetdv advised.