Does this same clip have audio when played in the media library? If it does then Click and Drag it to the timeline to replace it and check for audio. That clip audio may be missing the decoder needed if it is, say dolby digital 5.1.

You can check the Windows properties/detail and/or the PD20 show properties on that clip to find out. Alternative would be to use vlc or mediainfo to find out.

This clip have audio, I can hear it in the media library and in the timeline, I can change the volume level but I don't see the grapg in the audio track

Quote Hello,
Suddenly the audio graph disappeared even the audio level line is mooved up to the maximum.
The audio level is actually increased but I don't see it in the graph. Please see the attached file
Any help will be appreciated

What would I do in your place.
1 right click, select Regenerate Waveform
2 right click, select AudioEditor
Check if you need to turn up the volume
Make a small change so that when exiting a new audio file will be created, this should correct it.

This has been an increasingly large problem for me recently as well - I wrote my own topic about it here: https://forum.cyberlink.com/forum/posts/list/86256.page#357065

And was redirected to: https://forum.cyberlink.com/forum/posts/list/77471.page#post_box_317503 which has some ideas for correcting it. I can just about get it back sometimes with the ways listed, but I haven't found a 100% reliable workaround.

Thank you all for the useful information