British Land, the developer behind the Leadenhall building (the skyscraper's official title), reckons the reason bolts keep snapping is "high exposure to hydrogen" - but made clear that there is "no adverse effect on [its] structural integrity".
There's no word on when the bolt actually snapped - British Land just said it was "recent", but the last time this happened was November, when two steel bolts snapped and fell to the ground days apart, prompting the skyscraper to install "precautionary tethering", which caught the bolt this time.
British Land said it was planning to replace similar bolts on the 73-storey building "as a precautionary measure".
The news was unfortunately timed, coming at the same time British Land said it had leased more space in the building, meaning 70 per cent is now under offer.
Last year it became the most expensive office in the City, when insurance group FM Global agreed to pay £85 per sq ft for the entire 41st floor.
How London's tallest buildings stack up
The tallest building in London, The Shard, is over three times smaller than the world’s tallest building, the Burj Khalifa, which stands at 829m (2,719ft) tall. The Burj Khalifa, located in Dubai, opened in March 2014.