Render Visualforce page as pdf and attach to email, pdf attachment not showing data/values

Here is the Visualforce Page:

<apex:page standardController="BPA__c" renderAs="pdf">
<h1>Here's a copy of your BPA</h1>
<p>Thank you, <b><apex:outputText value=" {!BPA__c.BPA_Signer__r.Name}"/></b>, for 
   joining Our Network!</p>
<p>BPA Signed Date:&nbsp;
        <apex:outputText value="{0,date,long}">
        <apex:param value="{!BPA__c.BPA_Signed_Date__c}"/>
        </apex:outputText></p>
</apex:page>

Here is the Apex Class:

public class sendAnEmail {
    @InvocableMethod
    public static void sendEmail(List<Id> lstId){
        List<String> EmailIds = 'emailaddress@email.com'.split(',');
        PageReference ref = page.bpa;
        Blob b = ref.getContentAsPDF();
        Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage();
        Messaging.EmailFileAttachment efa1 = new Messaging.EmailFileAttachment();
        efa1.setFileName('attachment_BPA.pdf');
        efa1.setBody(b);
        String addresses;
        email.setSubject( 'BPA PDF' + String.valueOf(DateTime.now()));
        email.setToAddresses( EmailIds  );
        email.setPlainTextBody('Hey there, Thank you for Joining the Network!');
        email.setFileAttachments(new Messaging.EmailFileAttachment[] {efa1});
        Messaging.SendEmailResult [] r = Messaging.sendEmail(new Messaging.SingleEmailMessage[] {email});
    }
}