Missing Audio on Export, totally stumped. HELP

I have two files which were downloaded as recordings from Microsoft Team. Audio is present throughout the clips. However, when placed into the timeline, no waveform is present for certain sections. BUT--when skimming through those sections with no waveform, audio is there. However, when creating an output file, the areas which have no waveform, have no audio. I have done the following:
trashed preferences
trashed and started new library, event, project
re booted FCP, re booted iMac
Tried importing the affected files into new timelines
placed files FIRST on desktop, then changing the audio codec before importing
Nothing has worked. These files have 16Khz sample rate, not 44.1 or 48 but I am stuck here and would appreciate any help. Attorney at fed agency needs these files soon. Thanks all!

OK, here goes. I did a quick test by making an mp3 file at 16kHz which seems to come good in FCPX this way. For quickness I had to do it in High Sierra and 10.4.6, but should work in the up-to-date version.

Open the 16k audio file in QT Player. It should open and if you play it, it will sound very slow.

Choose File/Export As/Audio Only... This will make an m4a file of the audio and the sample rate will still be 16k. This is just so that we get FCPX to see the file.

Make sure the audio is set to 48kHz for the Project, and drop the new m4a audio file into the Timeline. The audio will appear to be three times as long as the original – don’t panic yet! Select the audio clip and choose Modify/Retime/Custom Speed... Change this to 300%.

Go back to Modify/Retime and deselect Preserve Pitch near the bottom of the menu.

You should now hopefully have useful audio.

Apologies. In my hurry to help, this method drops audio to make the clip shorter. Good try...

Thank you all the same. The file comes in at 16Khz, m4A.

Project Properties were set at 48kHz. It is puzzling to me how the file plays fine inside the timeline in FCP, then once created as an output file, the information is lost. I have tried all manner of settings in creating the output file as well.

In order to mitigate my previous mistake, in my haste the way I made a 16kHz audio file was, shall we say, flawed.

I have now made a proper 16kHz mp3 audio file. This does work in a Timeline just fine, but maybe your Teams file is slightly 'Microsoft' in nature.

If you can open the file in QT Player, do the Export as I previously said to an m4a and FCPX should take care of it. The file will still be at 16kHz sample rate but Core Audio makes it playable.

Sincerely hope this helps.

I am not sure. The file is already 16k. I have tried re-encoding it. The file inside FCP plays fine. but only on output, is PART of the audio missing.

Hello, I have same problem- also with MS Teams record. Did you solve it? Thanks

Did not, had another editor who was able to resolve using Premiere. This is a weird one.