I have found a solution that worked for me without restarting (although restarting worked before when this happened)
My problem was that both the Hot Key
or the contextual menu Right-Click
-> Speech
-> Start Speaking
did not work within any application like Chrome
and Text Edit
When I went to System Preferences
-> Accessibility
-> Speech
-> Play
the button toggled to Stop
as if playing but I heard no audio.
My Solution: I switched my default voice from Heather Infovox iVox HQ to Samantha then pressed the Play
button.
I got audio.
Then I switched back to Heather and both Hot Key
and contextual menu Right-Click
-> Speech
-> Start Speaking
worked without quitting any apps or restarting my computer.