Lead data not captured after filling out form

I just encountered a second instance where leads are filling out a form on one of our pages but none of the information is being captured in Marketo. Has anyone experienced this? It's occurred on two different pages, that are used for events, but it doesn't happen all of the time. I've only made text edits to the page so I'm not sure what might be causing this to happen. We're not able to find any lead information in Marketo from during the most recent event the page was used for. Thanks!