Audio and FPS issue

I've had issues in the past with "Fix Audio Problems" in FCP's preferences before so I always leave it off now. Is that on?

Preferences > Import > "Fix Audio Problems" near the bottom. Is that on? If so, what happens if you turn it off and import one of those clips and test?

Have you tried the clip with audio in an integer frame rate timeline like 24fps?

What are the complete specs of the media, video and audio? Does it use variable frame rate? Check the specs using MediaInfo or Invisor.

Fractional frame rates are no longer necessary. I'd choose a non-fractional frame rate like 24, 25, or 30fps depending on what you want to accomplish.

Have you togged Preserve Pitch off?

Change clip speed in Final Cut Pro for Mac - Apple Support

I would have thought if you were shooting at 50fps you should be using a timeline of either 50fps or 25fps.

Why would you want to use 23.98fps?

If you play back your video in slow-motion your voice will sound weird.

Is there any way you could share a clip so others can test?

Audio is created and processed by sample rate, not by frames per second, thus FPS should have no bearing on audio as long as it's all 48kHz both in the file and project settings. I've read somewhere else about a similar issue with a GoPro. I'll have to see if I can find that thread again. But I seriously don't see FPS settings effecting audio playback.

Please use either of the apps I mentioned to give complete details.