Let's take a look at one of those files. Is what you describe occurring on the timeline sequence, or after exporting to a file?
What version of Videopad is being used? Here's how to upload and share the file...
Please share a file or two that has the issue. Someone will check it out. Upload the file/s to a free server, such as Google Drive or MS OneDrive, get a shared (public) link, copy the link and paste it here or to me in a Private Message via the mail envelope in the top-right corner of this forum. When using Google Drive, if necessary change "restricted" to "anyone with link can view."