Hi Andrew, could it be, by any chance, that the track you want to play with is not armed for recording? If not armed, you won't hear any sound when playing on your keyboard, even if you see midi data flowing, as you mentioned in your screenshots.
The arm button is the one looking like a rec button next to the vumeter, if this button is red , arm is activated.
Please note that in Ableton standard settings ( in preferences / record/wrap launch) Arm and Solo buttons are set on "exclusive" meaning that only one track can be armed or soloed at time.
Maybe during your experiments , solo and arm were on exclusive mode, and arm was already busy on another audio or midi track.
Hope this helps,
best,