When generating certain phrases using certain words some of the new neural voices end up having a glitch in the sound file. The words are pronounced correctly so it makes us believe it is a technical error that needs to be ironed out. We are able to fix the issue by adding quotes to the phrase.
You can experience the issue for yourself by using these neural voices - Ashley, Cora, Elizabeth, Michelle, Monica and others. If you use Sara, Jenny and others the phrase does not have this glitch.
Phrase:
Thank you for calling Martin.
Is this something you are aware of and are working on?