This is not a regression as the TTS plugin isn't available in 4.27.2.
Text to Speech does not work in Play in Editor, but does work in Stand Alone.
A warning is thrown:
Changing the Channel ID still results in a warning.
The text inputted into the 'Speak on Channel' plays over audio.
No Text to Speech sound is heard. A warning is thrown in the Output Log:
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-161327 in the post.