Audio dropping out on import

Hi, I've finished a short film that just needed some text added. I don't have access to the original session so i just imported the mp4 file into the timeline to add the text but the audio drops out, i've tried to do the same on another computer with fcpx and I'm getting the same scenario, any thoughts on why this may be happening?

best
S

I should add, it's only part of the audio that drops out, and i cant see a waveform at these points.

Some possibilities:
1. The computers can't playback the compressed mp4 file smoothly - try switching in the viewer from "Better Quality" to "Better Performance" .
2. Maybe you didn't allow the waveforms to completely draw before closing FCPX. If it's not much trouble, delete the library, create a new one and import the mp4 file again being sure to wait until the full waveform finishes being created.
3. Check import settings and in the audio section try turning off "remove silent channels".
4. Maybe the original encode to MP4 was faulty. Do you have any copy that plays the missing audio in Quicktime or another app besides FCPX?

If none of the above helps, let us know what OS and version you are using, what version of FCPX, what the computer specs are and what the original codec is inside the MP4 file. Also whether you optimized the media upon import and if you have tried deleting FCPX preferences (Close FCPX - Hold down OPTION and COMMAND when you restart FCPX and follow the prompt to delete preferences).

Thank you. I'll troubleshoot those suggestions.

So, stupidly I hadn't checked the film again before importing it, it's got audio dropping out also on that the mp4 H.264 aac file.