It's likely that the page is not different, just "updated", like if you fixed a spelling error on your blog post after it was indexed. There will be a lag where the index is different from the content but google can re-crawl and get the same content.
I believe the paywall is turned on and off consistently for all clients, probably not violating terms.
I believe the paywall is turned on and off consistently for all clients, probably not violating terms.