Elements 2018 - Some clips add to timeline without audio

Hi Everyone,

Contextual Details as follows:

Video source was a GoPro. (MP4)

Clip has been confirmed to contain audio

Previous 32 clips are from the same source and shot on the same day.  All 32 added to timeline ok, with audio and audio waveform visible.

Clip 33 added to timeline without audio or waveform

Clip 34 is ok and contains audio and waveform

Clip 35 and 36 are missing audio

Clip 37 to 41 all have audio and waveforms

Windows 7 PC

Previous movie had no problems

Why would PE2018 discriminate like that?

Could file corruption make PE drop the audio only?  (I think this is unlikely considering the audio plays ok in another player)

Here is a screen shot showing the clips with the missing audio.

Thanks for any help.

Regards

Jason