Erratic on the timeline or only at export? What are the export settings? Have you tried exporting at sightly lower resolution?
You might test this release. For licensed users upgrades are free for up to six months from purchase date. After that, VP will continue to fully function but a fee will be required in order to register the newest. Retain your old install file and registration info.
THE best way to demonstrate the issue is to share the project. This is easy, takes little time and can be private. Folks here will help; fixes often come quickly.
Follow these steps, and we'll take a look...
1. With your project on the timeline, click on MENU at the top-left. Click FILE|BACK UP PROJECT FILES TO FOLDER. Choose a folder and SELECT FOLDER.
2. Locate the saved, numbered folder. No need to upload the export or VPJ files. Upload it to a free server - Google Drive, MS OneDrive, etc.*
3. Get a shared, public link. If using Google Drive click GET SHAREABLE LINK. Change "restricted" to "anyone with the link can view" Then click COPY LINK | DONE.
4. Paste that link here, or click the folder at the top-right of this forum and privately message it to me. It won't be shared.
* Before uploading, right-click the folder, click PROPERTIES. Look at the File Size to confirm that it's not too big for the free space on the server.