Elon Musk made expanding Twitter Blue a focus after his takeover in October, and chief among the changes was allowing everyday users to get a blue tick - a feature previously reserved for verified accounts.
Twitter has announced that subscribers to its premium Blue service can now post longer tweets - but the news has been overshadowed by technical glitches.
Customers who pay £8 a month can now benefit from a 4,000-character limit - substantially more than the standard 280 characters for those with free accounts.
But some users were unable to tweet at all on Wednesday, with thousands encountering a message that said they were over the daily limit for posting.
One of those that did manage to get a message out was Twitter Support, which said: "Twitter may not be working as expected for some of you. Sorry for the trouble. We're aware and working to get this fixed."
This is the latest bug that the social network has suffered since Elon Musk's takeover late last year - with the billionaire quickly deciding to lay off a substantial number of staff.
Critics have long questioned whether Twitter's service would remain reliable with fewer engineers.
Twitter has admitted that longer tweets could have resulted in a lot more scrolling for users, but said: "Don't worry, Twitter is still Twitter. We know longer tweets could mean a lot of scrolling, so they'll be capped at 280 characters on your timeline and you'll see a 'show more' prompt to click and read the whole tweet."
In other developments, Twitter users also reported that TweetDeck - a social media dashboard app that allows users to create multiple feeds tailored to subjects they want information on - had also gone down.
The free service, which is accessed via a separate webpage using a standard Twitter account, is particularly popular with journalists and businesses.
Screenshots appear to suggest that TweetDeck will soon be a feature exclusive to Twitter Blue, but the company is yet to make a formal announcement.
Elon Musk made expanding Twitter Blue a focus after his takeover in
October, and chief among the changes was allowing everyday users to get a
blue tick - a feature previously reserved for verified accounts.
That move quickly descended into farce as pranksters impersonated the likes of ex-president George W Bush, former prime minister Tony Blair, and the official page of gaming giant Nintendo.
It forced Twitter to pause the service, which was relaunched in December after a month on ice.