Importing edited Mbox file from Gmail - Manipulation test

I am testing the theory behind manipulated emails and what forensic evidence can be obtained. I notice that when Google Takeout is used to export emails from a Gmail account and are subsequently edited (in this case, the body text), SPF alters from "PASS" to "NONE with IP 0.0.0.0" and DKIM completely disappears in the "Original Message" view, however the headers remain unchanged with the exception of the edits to the body text. The unedited email indicates SPF as "Pass" and DKIM as "Pass" (first image). This changes in the second image once any alteration is applied to the original email. Before importing the email via Thunderbird, I delete the original email in Gmail (including the trash) and then load the manipulated email to Thunderbird and subsequently to the Gmail inbox. Is there an explanation for the change in SPF and disappearance of DKIM to the manipulated email?