Edits on PDF files disappear afte signing document.

Hello everyone, we've been encountering the following issue with Acrobat Reader:

We have a PDF form that three people fill (one at the time) and the last person has to insert a signature before sending the document somewhere else. First person fills his part and sends it to the second. Second person fills her part and sends it to the third person. The third person fills her part and inserts a signature and here comes the issue. Whenever the third person signs the document, all the edits of the second person disappear. We've been trying for a while now to fix this issue, everything was working fine previously but for the past couple of weeks it's been doing this. It happens only with the second person. Anybody ever experienced the same issue? Any tips on how we can fix this? All our Acrobat versions are up to date so we really don't know what to do anymore, we even tried upgrading to Acrobat Pro but it still didn't solve the issue.

Thank you!