No audio when playing timeline and then crashes when trying "saving as"

Ardour 6.9.0 (from ppa) crashed after I exported to mp3. After that, I was able to open the project but I cannot hear any sound by playing the timeline (though I can still export to file and hear it playing normally in VLC). Then, I decided to remove Ardour 6.9.0 (from ppa) and installed Ardour 6.9.0 (from Ardour) with installer. Unfortunatly, I still can’t play and hear any sound, besides Ardour crashes just like before. I am running Ubuntu Studio 20.04. Please, what else info may I provide you with? Thank you.

In the mixer-window, does the master-bus meter show a signal when you play?

…and if so, is the master-bus’ output connected?

Yes, the absence of sound happened because of the layer output routing got misconfigured after the crash. Thank you.