Weird.
Could it be the case that your share count doesn’t get updated because you are logged in on your site or a cookie blocks the update process?
And doesn’t it update the count for every social media channel you offer or only for Pinterest?
Did you check with the browser history cleared and all the usual stuff?
Perhaps trying it via a vpn connection and a “private” browsing session?
If needed you could contact ET and ask them what might be the problem.
Sorry that I can’t be of any real help, but I will try and see if I can dig up an old twitter account. Perhaps that may help in testing and troubleshooting.
Let me know!