Different audio after export a video

Hello, I had a weird situation while editting my video.

I have a video clips recorded with my camera and added a background song as a separate track.

I used a Remix tool [R] to change the song's duration. It worked ok. But I needed to manually lenghten the audio for a 3 seconds, so I used a razor tool in 2 points (like in and out) and doubled the desired part of a song. 

In the preview everything was ok, but after export, from the moment when razor was used I hear totally different part of a music, and it's not ok till end of the clip. (First part of a clip is ok)

I workaround that by rendering only a audio track and replacing the "original one" with the exported remixed and lenghten one - and it works ok, but still - IDK why it's not working with the 'original files' 🙂

Computer used - Macbook pro M1 2021 16gb ram