Piano roll not working

Aloha from Honolulu,

It used to be that if I opened, say, a piano MIDI track in the PIANO ROLL, I could select three notes that make a chord and hear the chord, in addition to having LProX identify the chord.

Now, LProX identifies the chord, but there's no sound.

Similarly, I could "play" the vertical piano at the left of the piano roll and here notes.

Now, silence.

That said, if I play my song, the the MIDI track plays fine: I can hear all the chords.

Something tells me I've clicked / turned-off something accidentally... and I don't know what it is. Similar concerns in the forum are from many years ago.

Any thoughts?

I can keep keep going as is, but it's super helpful to be able to select-play notes in the piano roll.

Mahalo!

Cat