Here's the official changelog for Tweetium v4.2.502:
This update addresses Twitter's shut down of the Streaming API used by the app and the Pro subscription services.
- The app will now only support polling every minute to refresh. More configuration of this and improvements to refresh behavior will come in a future update.
- Currently, purchase of Pro subscriptions is disabled, as push notifications and Connect+ are no longer possible with the Streaming API shut down by Twitter. If you've previously had a Pro subscription, the app should continue to let you make use of multiple accounts. In the future, some variation of the Pro subscription option may return (TBD).
- Fixed a bug where clicking on suggestions in the tweet composer would not add them correctly
In fairness, if Tweetium is your app of choice to while away time sitting on the toilet waiting in a queue, then it'll still work fine. Auto-polling of Twitter's APIs every minute mean that tweets are more or less real time and there's always something happening, plus you can manually refresh whenever you like. But then you can do much the same with the free official client, which is updated server-side with new Twitter features, making the use case for Tweetium a lot less strong.
It's a crying shame, and for once the issue isn't with Windows 10 Mobile, it's a third party change. Twitter has every right to do what it likes with its own platform/service, of course, but the API changes won't endear it as a communications system for existing Windows 10 Mobile users.
What I don't understand is why Tweetium can't detect a new DM on a background refresh and then trigger a toast, etc. Maybe something like this can be worked on for a future update? Or perhaps it's just too crippled, as it would fall back to every 20 minutes, as is typical with background processes under Windows Phone 8.1 and Windows 10 Mobile - and who wants a 20-minute-delayed DM?
As usual, Tweetium is a commercial UWP application and is about £2.50 in the UK Store, but well worth it, and works on phone, tablet, laptop, and so on. Just be aware that DMs won't now ping your phone and that you should either seek other messaging systems (SMS, Whatsapp, Telegram, etc.) or switch to the Twitter client on another platform. Shame.