Under OPTIONS | DISK tab, Clear Unused Cache Files.
Check out this article... https://www.nchsoftware.com/videopad/kb/1772.html
Save Project File AS routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. From the HOME tab, that choice is available by clicking the chevron to the right of the Save Project button on the toolbar. That way, you are protected.
If the issue persists, we need to see the project just as you see it. The process is easy, quick and can be done privately. Just follow these steps...
Back up --- 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.
Upload --- Use a free server - Google Drive, MS OneDrive, etc.* - to upload the saved, numbered FOLDER. Do NOT upload the individual VPJ or export file.
Get link --- Get a public link. If using Google Drive click GET SHAREABLE LINK. If necessary change "restricted" to "anyone with the link can view"
Share --- Click COPY LINK | DONE. Paste that link here, or click the folder at the top-right of this forum to message it privately 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.
You are not out the cost of the update, which should be superior to your older version. Still, it can be reinstalled and a refund can be issued.
If you make the effort to share your project, someone here will be glad to help correct the problem.