Utilization of GPU is being improved. It's wise to run the latest version. 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.
Some basics: Load only the files that will be used in the project. Allow the timeline to fully cache (green line above the thumbnails) prior to editing. Under OPTIONS | DISK tab, Clear Unused Cache Files, to eliminate possible corruption. Do that before beginning a new project.
Under OPTIONS | EDITING, toggle Use Hardware Acceleration to see if that makes a difference.
Verify that your video driver and Direct-X are current. https://www.nch.com.au/kb/10265.html
Look into proxy editing, where small-resolution files are edited, then the originals substituted for export.
Breaking a project into more manageable segments, exporting each, then merging them for the final export may help.
If export isn't accurate, use the MPEG4 compressor in lieu of H264. Or export at lower-res.
Of course. 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. Then you can restore a project to the state it was in when saved. Just double-click the VPJ file (which isn't playable).
If you like, someone will analyse your project. Uploading and sharing is not difficult, takes little time and can be private. Just follow these steps...
1. 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.
2. Locate the saved, numbered folder and upload it to a free server - Google Drive, MS OneDrive, etc.* (Don't upload the export file or only the VPJ.)
3. Get a shared, public link. If using Google Drive click GET SHAREABLE LINK. Click the blue "Change to anyone with the link..." Then click COPY LINK | DONE.
4. Paste that link here, or click the folder, above top-right in this forum, and message it to me. This is private and 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.