The news came in a statement posted to Paramore's Instagram story: "Due to unforeseen circumstances, Paramore can no longer attend and perform at iHeartRadio ALTer EGO," the group said. "The band apologizes for any inconvenience."
No other explanation was offered, which made fans on the r/Paramore subreddit nervous.
"I really hope they are fine health-wise as well as nothing serious happened in their personal lives because I can't think of any other reason to cancel a festival appearance," one said. "I'm thinking exactly the same. It has to be something more personal and not about the contract that ended," another added.
The cancellation comes just days after Paramore wiped most of its social media accounts. The move followed Paramore completing its contract with longtime label Atlantic Records. This led some fans to speculate that the band was breaking up.
Paramore provided their fans a cryptic update in another Instagram story last month.
"Now that Paramore has spent the year touring behind This Is Why (and making sure to take better care of themselves while they're at it), a chapter of the band's career has come to a close," said the text gleaned from an UPROXX article.
"They've now fulfilled all label obligations (to Atlantic Records) and are effectively free agents. As for the future of Paramore, all three members agreed that there's a level of uncertainty."
The message also had a link to the full interview, which included more details.
"The only thing that matters is we will still get to be each other's community," Williams told the outlet. "I just hope we can keep building the Paramore empire and then rule the world," drummer Zach Farro added.
The band is currently scheduled to tour with Taylor Swift in Europe later this year. The trek will begin in Paris on May 5 and end in London on August 17.
Swift has been friends with frontwoman Hailey Williams since the two were teens. The pair met at the 2008 Grammys when both were nominated for the Best New Artist award. They were introduced by Swift's mother Andrea.
"We were at some Grammy party — it was actually Timbaland's Grammy party," Williams said during an October interview for The Tonight Show Starring Jimmy Fallon.
"Huge. I was very nervous, but a woman came up to me and she said, 'I'm Taylor Swift's mom and, you know, Taylor doesn't have a lot of friends her age that do music. And I would love to, like, you know, introduce you guys or get your number.’ Andrea, the legend that she is. She connected us."