You should never lose your work if you back up routinely and do not move or delete any source files. Always Save Project File AS, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. Save AS creates a unique VPJ control file that can be double-clicked to load the project.
Under OPTIONS | DISK tab, Clear Unused Cache Files and see if that resolves the issue. If not, update to the latest. 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.
If problems persist please share your project. Someone will take a look and come up with a fix. 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.