Response from change.org

However, there are some reasons why some signatures might not count, or be removed, such as the following:

Sometimes it may take around 24 hours for a petition to update with new signatures
If someone is signing a petition for the first time, they will also need to confirm their email address, if they don't confirm their email, their signature is removed
If more than one person tried to sign from the same device or IP address, their signature might not be counted or be removed
Signers can also remove their signature at any time through the link in the confirmation email
 

If you have signed the petition and received an email from change.org to verify your email address please do. As of right now there's over 120 signatures that seem to have disappeared.