The EU has published its latest data on social media platforms reviewing hate speech.
Twitter reviewed half of its reports within 24 hours, compared to 82% last year, and removed fewer.
The company recently shut down its Brussels office which helped it comply with EU laws.
Twitter is removing less hate speech and taking longer to review it, according to a European Union report on social media companies.
Its data says Twitter reviewed roughly half the reports it received about illegal hate speech within 24 hours, compared to 82% in last year's study, which took place in a six week period in April and May, several months before Elon Musk's takeover.
The proportion of posts removed has also fallen, dropping nearly five percentage points to 45.4%.
The data published on Thursday is the seventh report from the EU's yearly study to see how social media platforms are complying with its laws on disinformation.
It sent over 3,600 notifications of hate speech to six companies, which also included Facebook, TikTok, and Instagram. Facebook received the most at 1,558, while Twitter was the only other company to see more than 1,000 hate speech reports.
Since Musk took over, Twitter has seen companies and politicians impersonated thanks to his plan to allow anyone to be verified for $8 per month, a plan that is currently on hold.
The Washington Post also reported that the use of the N-Word surged nearly 500% in the 12 hours after Musk's deal was completed.
The same day that the EU released its data, the Financial Times reported that Twitter shut down its Brussels office, which was responsible for ensuring Twitter complies with the region's disinformation laws.
Twitter's European digital policy chiefs were the last two remaining in the small office after Musk laid-off half of the company's 7,500 staff.
The Brussels office was then left with no employees after Musk sent a midnight ultimatum to all staff, telling them to commit to "long hours at a high intensity" or get three months of severance.
Facebook, YouTube, Instagram, and the French gaming site Jeuxvideo also reviewed less hate speech reports within 24 hours this year. Only TikTok improved its performance in that category.
YouTube was the only platform to improve its removal rate of hate speech this year, going from 58.8% to 90.4%.
The EU vice-president for values and transparency, Vera Jourova, said: "It's worrying to see a downward trend in reviewing notifications related to illegal hate speech by social media platforms."
"Online hate speech is a scourge of a digital age and platforms need to live up to their commitments, including by dedicating sufficient resources, to make the online world safer for everyone," she added.
Twitter and Meta did not immediately respond to requests for comment.