Version 12.12 is a beta test. Install this version instead. There's never a mandate to change versions. If yours is working well, consider sticking with it until a regular release has been out for awhile. The latest can always be test driven, to see what's new or changed.
If that doesn't clear up the issue...
Close the program, restart. Before loading anything, go to OPTIONS | DISK tab and Clear Unused Cache Files. No change?
Close Videopad, then right-click on its executable (the launch file) and Run As Administrator. 
If still no joy, please share the file, and we'll 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."