Hello, Punchydude. Thank you for posting your question to the Apple Support Communities. We know that being able to use the narration features in Keynote must be very helpful to you, and we’re happy to help however we can.
From what we gather, you are only noticing this issue after you pause, and then resume recording. To get started, we would like to provide you with the suggested steps to use when recording narration with Keynote. If you haven’t already, please read over the following Apple Support article:
Record audio in Keynote on Mac - Apple Support
If the suggested steps above are not producing the expected results, we can help you more. To isolate this issue, can you tell us how you are recording the narration? Are you using an external microphone, or the built-in microphone that your Mac has?
When you record audio with other apps, such as the Voice Memos app, do you notice any similar issues? This last article can help you get started with Voice Memos:
Create a recording on Mac - Apple Support
We hope that the information in our reply helps you get started on finding a solution. Please let us know if we can help you further with this.
Cheers!