[BUG] iOS players no longer appearing in Plex Web's cast drop down

I'm no longer able to control and fling media to iOS devices from the Plex Web App.

iOS Plex App is updated to the latest version. Plex Media server is running on Linux and is also up to date - version 1.3.3.

I'm able to fling media from iOS app to iOS app, running on a different device. I can also fling media from iOS to Plex Web App.
Other Plex Web App instances, Plex for Playstation appear in the web app, only the iOS players are missing from the drop down.