Weird audio/video sync after sending the file to the client

So i have working with a certain client for the past year.

I always use (project manager) to send him the files so he can do one last check before render

but this month we have been working on a big project of 9 videos, what is clearly weird is that after i send him the files, when he opens the PR project, the audio is clearly out of sync 

while my version is working just fine

We have a shared OneDrive folder where we upload/edit our files, so we both always have the same file 

we also have the same PR ver. (15.2 build35)

(below an example of this issue )