Fix iCloud Drive Sync

My iCloud Drive has stopped syncing on my Windows PC. I have already gone through the advanced checks—re-installing iCloud for Windows, signing out and back in, resetting network settings, and even deleting the iCloud cache folders—yet new files refuse to upload or download... (Budget: £10 - £20 GBP, Jobs: Computer Repair, Microsoft Exchange, System Admin, System Administration, Technical Support, Troubleshooting, Windows Desktop, Windows Server)