Hi,
that means, in the protocol block, you didn't see anything like "2017-08-31 17:55:21 PayPal IPN paid"?
Could you pls confirm it? If that is the case, i think i can focus the issue and take quick investigation.. (For some reason, I can not test PayPal IPN right now)
This part was modified by other developer due to the last PDO update.
Also pls take a look at a previous booking which was paid by PayPal (before the last update) and check the protocol there, you should see something like "xxxx-xx-xx 17:55:21 PayPal IPN paid".