Have you tried uninstalling/reinstalling IF? Maybe even try to restart your device and see if that fixes it.
Edit: Does the audio act up on other apps like youtube or social media? Or does it only happen on IF?
Edit #2 If it only occurs on IF it could be a text to speech issue on your device(I believe IF uses text to speech for ATC commands, if not this won’t work). Go into settings look up text to speech and then change your primary engine and see if that works.