Online tools often fail during bulk CSV to VCF conversion because they have file size limits, upload restrictions and weak processing power. When you try to convert thousands of contacts at once, these tools may time out, skip fields, or even stop the process midway. I faced similar issues with missing names and incomplete phone numbers. Thats why I switched to a desktop solution. Softaken CSV to VCF Converter handles bulk files smoothly without size limits, keeps data secure on your system, and allows proper field mapping and preview. Its a more reliable solution that works completely offline. Best for large contact conversions, and try the demo edition for more.