Debug missing web to lead records

Is there any way to debug problems with the Web to Lead process? We seem to lose records randomly and don't know why.

All records are saved in a text file on our Web server before we try to post them to Zoho CRM. Mostly it works, but once it a while it doesn't. Over the past week we've had three records not make it into Zoho CRM. There's nothing obviously wrong with the data.

It's very annoying to have to look these up and enter them manually. Almost makes the whole process worthless. If we simply import them at least we wouldn't be wondering.