Voice output alters when using tag <say-as interpret-as="characters"> in POLLY

Amazon Polly question.

I have a sentence, such as "it will be OK."

When I change the script to "It will be <say-as interpret-as="characters">OK</say-as>. "

or to

"It will be O K. "

The output sounds muffled for that sentence only, then goes back to how it sounded in the rest of the script.

I'm using:

• Neural engine
• English, US language
• Matthew, Male voice
• SSML turned on

The same thing happens when I use any 'interpret as=' tags

Is anyone else running into this issue? It's very distracting and I can't figure out why it is happening.

Thanks for any help you can give me.