Problème d'exportation

Never easy to troubleshoot premiere problems from a distance so please tell us your system specs: OS version, Premiere version, amount of RAM, Hardware specs including graphics card and if you have any 3rd party plugins installed for Premiere... Also, sequence settings and clip properties can also help. Although you can throw almost any format into premiere, some formats can be problematic, particularly on an underpowered system.  And by any chance are any of your sources from a smartphone or a screen capture?  If so, the problem maybe that you're dealing with sources that have a variable frame rate which can have intermittent and unpredictable problems.  Here's how to diagnose and fix the problem

use mediainfo to determine whether your source is variable or constant frame rate
https://mediaarea.net/en/MediaInfo/Download
if it's variable use handbrake to convert to constant frame rate setting the quality slider in the video panel to maximum or use shutter encoder https://www.shutterencoder.com/en/ which allows you to transcode directly to prores or other mezzanine formats, "First choose a video codec.
Then in the "Advanced features" section check the box "Conform by:" and set your frame rate in images/seconds." from ShutterEncoders FAQ. You want to figure out what the original target frame rate of the smartphone or screen recording was and set to that in the conform dialog.