The engine used to recognize the phonemes and convert them to the 9 mouth cue types is
Daniel Wolf's Rhubarb Lip Sync application.
The add-on ships this CLI ( command line interface) application as part of the installation zip file in the bin folder.

The rhubarb lipsync NG is a complete rework of the original rhubarb lipsync addon based on the same principles and ideas.

Github is the preferable place:

• Search Opened issues. Maybe somebody has already reported the same issue.
• Also search already Closed issues. There might be similar issue with a solution from the past.
• Follow the Troubleshooting guide.
• If still no luck or you have some suggestion/question/feature request open a New ticket

You can also use the inbuilt product-support of the blendermarket.

The NG in the name stands for Next generation. This is to distinguish this reworked addon from the original one.