I have the same problem....My guest checked out yesterday, and the review usually available on that day. However, the feature is missing and not able to leave review.
It;s been like this for about two months now - the invite now takes up to three or four days to arrive. I tried to contact Airbnb about it but silence is all I got back..
Same issue here. I'm slightly concerned, as it was the first time a guest did not seem too happy with their stay, dispite me probing them for more answers as to what their expectations were. Now the guest may think it's because of me that the review process is delayed. This will not be a fair score at all.