Missing Audio track after exporting

Hello everyone, I am really sorry if my question has been asked before, if it has please point me to the thread. I am a total beginner and have been watching some tutorial videos on editing. I am currently working on my first project which is to simply upload video footage to Youtube with my voice commentating,
I have made a 40 min clip with my voice talking during the video, i have watched the unedited video through the timeline and you can clearly hear my voice along with the video footage.However, when I export the video to mp4 to prepare for the upload to youtube i seem to have lost my voice audio. The video plays back perfectly but there is no voice over. Yet when i play the original before converting to mp4… it has my voice once again.

I am so sorry for asking but i have checked as many tutorials as I can find and i dont seem to see what i am doing wrong.

Any advice and help you can give me is greatly appreciated.

Thanks in advance.

P.S. This is not an audio voice over i have tried to add after the video was captured. It was recorded at the same time,

windows 7 starter 32 bit.
shotcut version 190816.
I have the same/similar problem.
i stitched three clips together in shotcut.
The exported file lost all audio at the junction of first and second clip and doesn’t return.
original files have audio, and as i saved the .mlt i opened it and found the audio intact.
It is just not being exported properly sadly.
Very strange that it is exporting audio for the first part of the video.

All the same file types etc as all filmed as one continuous shot on a camcorder but it saves the file when it reaches 2gb and starts a new clip.