Most people wait till the last days before registering and as such the system processes huge number of registrations. When this happens, some of the forms encounter errors during submission.
The DV lottery registration software is design in a way that does not alert registrants of errors. So you may think everything went right but the system had already rejected it even before date of draw.
It is recommended that you register in the early days and at time when your country’s internet is very fast. Slow internet does not load images correctly. Most images are received by the system truncated.