From what I can tell, this is happening only to you (I'm not getting notifications of anyone else getting unsubscribed for the spam flag). According to the Documentation, this is likely something in your email client flagging 070 messages as junk, which the system is reading so unsubscribing.
From the docs:
"Reviewing members who were removed because of reported spam
Some email providers notify Groups.io when group messages end up in their (the provider’s) users’ spam folders. Most likely, the group messages were automatically flagged as spam by the email provider rather than having been specifically marked as spam by the users.
When Groups.io receives such a notification, the system automatically unsubscribes that member from the group. Groups.io also sends the member an email with a link that lets them automatically and quickly resubscribe to the group if the spam flagging was a mistake. The email lets the member know to check their spam folder and mark any messages in there from Groups.io as not spam, which trains the email provider’s spam filters to make fewer mistakes about Groups.io emails."
As Steve has suggested, a review of filters in your client may be in order. Have you recently changed email clients?