No reports of this nature with 16.57, which is what you have. What are the PC's specs: CPU/GPU/RAM?
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, the AS choice is available by clicking the caret to the right of the Save Project button on the toolbar. That way you're protected, and shouldn't lose anything.
After doing that, close and restart Videopad and, before loading the saved project, go to OPTIONS | DISK tab and Clear Unused Cache Files. It's a good practice before starting a new project.
If problems persist, they can best be solved by you taking a few minutes to share the project, for analysis. Issues can be caused by a number of factors from editing errors to software bugs. Sharing is easy, quick and can be done privately. Just follow these steps closely...
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. No need to upload the individual VPJ or export file.
Get link --- Right-click the file and click SHARE. If using Google, right-click the file, click SHARE | SHARE. Change "restricted" to "anyone ... can view"
Share --- Click COPY LINK or OK | DONE. Paste that link here, or click the folder at the top-right of this forum to message it privately. 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.
If you prefer to check out older releases, go here. Ignore any virus warnings. There's never a mandate to update, if the program is working well for you.