This seems to be related to my problem from a couple of days back, but this time I know it is something at Twitter’s end…
Several of my users cannot find my app in their authorised app list ( https://twitter.com/settings/applications ) at all! I told them to de-authorise and then re-authorise my website. But it isn’t in their list!
I initially thought it was user error, but after some screen shots and seeing a couple in person that it is missing they were right!
I got them to log into my site with Twitter and then looked straight away - and it wasn’t there!