Maroon 5 say "technical difficulties" were to blame for their strangely lacklustre show at Chile's Viña del Mar festival on Thursday.
Singer Adam Levine appeared distracted and uncomfortable throughout his band's set, which was broadcast live on TV.
The star was "cold, reluctant and preoccupied," observed Santiago's La Tercera newspaper.
Broadcast live on Chilean TV, the set lasted a little over an hour, with the band playing a truncated, 15-song set.
A video shot as Levine left the stage was uploaded to social media and showed him complaining: "That was a TV show. That was not a concert".
The 40-year-old later explained that sound issues "impacted how I was behaving on stage, which was unprofessional and I apologise for that".
Maroon 5's name trended on social media during the concert, with many TV viewers criticising their performance.
"Adam sounds awful and he doesn't have the moves like Jagger at all," wrote Angelica as she watched the show in Nuevo, Chile.
"Love your music, but your show in Viña del Mar was disrespectful to every fan who paid and waited to see you live," wrote Ray Beron on Twitter.
"Lousy show," wrote another Twitter user in Santiago. "Haven't seen such unprofessionalism in a good while. There are no excuses for doing such a poor job."
Even politicians got involved. Francisco Undurraga, vice president of Chile's Evópoli party, who was born without three of his limbs, tweeted: "I apologise for the self-reference but Adam Levine has less voice and soul than my right arm."
Others were more forgiving.
"His voice is trembling," observed one fan. "Maybe something happened in his private life, we must be empathetic."
Llegó aquí como 25 minutos tarde, y pidió que nadie lo mirara a la cara, que se dieran vuelta hacia la pared, 🙄🤷🏽♀️— Denise Rosenthal (@NissRosenthal) February 28, 2020
A post by Chilean actress and singer Denise Rosenthal was retweeted 3,600 times, after she claimed Levine had "asked that no-one looked him in the face [and] turned to face the wall" as he entered and left the venue.
Chile's Viña del Mar International Song Festival is the longest-running music festival in Latin America, and combines live performances with a Eurovision-style song contest and other awards.
Ahead of the event, Maroon 5 had asked to play their set without interruptions, receiving their "seagull" awards backstage instead of on the live TV broadcast.
This was not an unusual turn of events, according to local media who said artists like Morrissey and Calle 13 had made similar demands in the past.
More problematic was their late arrival on stage, which meant TV presenters María Luisa Godoy and Martín Cáracamo had to "fill in for minutes that became eternal for those present," reported CHV news.
When they finally appeared, Levine was "evidently uncomfortable" and "his face showed no interest", CHV said in its review. When the crowd sang along to hit She Will Be Loved, the singer commented: "Well, if you want to do my job, go ahead".
In a statement to the BBC, the band's representatives explained the difficult circumstances surrounding the show.
"Prior to their arrival in Chile, Maroon 5 was informed by their representatives about civil unrest in country," it said.
"Despite this, the band insisted on going ahead and performing the show for their fans.
"Unfortunately, during the performance, the band encountered numerous technical difficulties throughout the show, including monitor issues and with both of Adam Levine's in ears," referring to the earbuds most performers wear onstage to allow them to hear the music.
"It created a very difficult situation for the band to deliver their normal show. The band loves their Chilean fans."
Levine also posted a two-minute apology to Instagram, which can be seen below.
- dijo que se dejó llevar por problemas que pasaron detrás del escenario por eso su actitud— 𝒎𝒂𝒓 ☁️ (@stylesvol94) February 28, 2020
- pidió disculpas por ser poco profesional
- apruebo convención constitucional
- dice que la banda valora chile y sudamérica#maroon5 #adamlevine #adamlevin pic.twitter.com/wLJ8cK35Zc
Footage from the concert appears to confirm the band's account. Although Levine was rarely off-key, his vocals sometimes seemed hesitant or timid during the early songs.
Things improved as the show continued, particularly during the 2004 song Sunday Morning, which sprang to life with a spirited solo from guitarist James Valentine.
Videos from inside the Quinta Vergara arena also suggest the 15,000-strong audience had a better time than those watching at home.
Known colloquially as "El Monstruo" (The Monster) for their ability to decide a performer's fate, the crowd sang along enthusiastically to hits like Payphone and Moves Like Jagger; and screamed in appreciation when Levine pulled a Chilean flag from his pocket during Makes Me Wonder.
The start of the 2020 Vina festival was marred by violent clashes between police and anti-government protesters; with masked demonstrators attacking shops and the O'Higgins Hotel, where many of the festival's technical crews were staying.
Although the red carpet opening ceremony was scrapped, the concerts have gone ahead amidst tightened security. Before Maroon 5, Ricky Martin and Pablo Alborán were among the headliners earlier in the week.
Puerto Rican star Ozuna will close the festival on Friday night.