While the band itself and its PR agency released statements on the 46-year-old's death, not many details are known at this time.
According to the band's Twitter account, The Cranberries were forced to cancel most of their European tour and all of their North American tour in September and October due to a "back problem" O'Riordan was experiencing.
"The outpouring of support The Cranberries have received from fans and followers during the past several months is greatly appreciated," the band said in a statement tweeted over the summer.
"Unfortunately Dolores O'Riordan's recovery from her ongoing back problem which forced the cancellation of most of the band's European tour this Summer has not been gonig as well as expected to such extent that her Doctors have now instructed her to cancel her upcoming almost sold out tour of North America with the band," the statement added.
The statement continued, apologizing to fans and writing that the band was disappointed in the turn of events. "Dolores and the band are very disappointed that it has come to this and send their sincere apologies to all fans and ticket holders, and hope to see you all again in the future when Dolores is well again."
It's unclear how significant, if at all, O'Riordan's back problem was in relation to her sudden death.
Hi All, Dolores here. Feeling good! I did my first bit of gigging in months at the weekend, performed a few songs at the Billboard annual staff holiday party in New York with the house band. Really enjoyed it! Happy Christmas to all our fans!! Xo— The Cranberries (@The_Cranberries) December 20, 2017
In December, O'Riordan tweeted from the band's Twitter account saying she performed for the first time in months at the Billboard annual holiday party.
"Hi All, Dolores here. Feeling good! I did my first bit of gigging in months at the weekend, performed a few songs at the Billboard annual staff holiday party in New York with the house band. Really enjoyed it! Happy Christmas to all our fans!! Xo," she wrote.
The band explained O'Riordan's back issue in detail in a social media post from June, writing that it had to do with her mid to upper spine, and that singing worsened her pain.
"Dolores' back problem is in the mid to upper area of her spine and the breathing and diaphragmatic movements associated with singing put pressure on the muscles and nerves in that area and exacerbate the pain. Sitting does not give any relief and at times in her case it can actually worsen the pain," the band wrote.
O'Riordan died suddenly in London on Monday while she was in town for a recording session, the band and its PR agency said. She was 46 years old. The Cranberries wrote that they are "devastated" by her death.
"Irish and international singer Dolores O'Riordan has died suddenly in London today. She was 46 years old," the band wrote in a Facebook post on Monday beneath a photo of the late singer. "The lead singer with the Irish band The Cranberries, was in London for a short recording session. No further details are available at this time."
"Family members are devastated to hear the breaking news and have requested privacy at this very difficult time," the group added.
O'Riordan led The Cranberries to worldwide rock fame for 13 years before the band took a break in 2003. They reunited in 2009 and were best known as a successful rock act of the '90s.
The Cranberries sold over 40 million records worldwide.0comments
O'Riordan wrote "Zombie," the band's hit protest song that reached number 1 on the charts in Australia, Belgium, France, Denmark and Germany. It won Best Song at the 1995 MTV Europe Music Awards.
O'Riordan also composed the band's first major hit, "Linger," which peaked at number 3 in the Republic of Ireland, number 8 in the U.S., and number 14 in the U.K.