I assume you mean Region FX- Melodyne, which uses the ARA protocol to move the audio to a separate audio stream in its own window.
If you play back the Region FX window you will only hear that audio, it is how ARA works.
If you start the CbB transport you should hear everything.
Region FX- Melodyne works as expected here.
As noted by others this is a Melodyne issue and separate to the main topic of this thread. Which is feedback on the Core product not third party plugins.
Please raise your Melodyne issue in a new thread thank you.