Numerous Twitter apps such as Tweetbot, with which users could access the online service, suddenly stopped working.
The software has not been able to connect to the Twitter interfaces since Friday.
Customers of the apps must use it to access the official Twitter app or the web version.
Until Saturday, it remained unclear whether it was a malfunction or whether Twitter's access was intentionally cut off.
The developers of the apps Tweetbot and Twitterrific wrote to their users that they were not getting any answers to their queries from Twitter.
The apps are affected differently: Tweetbot, for example, does not work on all devices, while Twitterrific no longer runs on the iPhone, but still runs on Apple's Mac computers.
The Fenix app works on iPhones, but no longer on Android smartphones.
Twitter makes its money with advertising: In its own app and the web version, users are presented with paid posts between the tweets they have subscribed to.
There are no ads in the third-party apps that have been with Twitter practically from the start.
Thus, Twitter earns nothing when users access the service there.
New Twitter owner Elon Musk has emphasized his focus on making money since advertising revenues plummeted after his takeover.
Musk, who had promised more transparency, has not yet commented on the situation surrounding other providers' Twitter apps.