Tweet for a user sent from my app does not apper in the users feed but no 403 error received


I have an app that has been working perfectly but a user complained that some of her tweets are missing.
When I checked all of her tweets were marked as sent i.e no error received from the POST statuses/update
If they failed I should have received a 403 error.
I am fairly sure my code is ok as I do receive 403 errors for users that attempt duplicate tweets.
So to me this looks like a twitter issue not publishing tweets that it has accepted from an app.
This only happened between 05:15 and 16:30 today.
Why would the tweets not appear, could it be an intermittent fault with the twitter API?