Sources with direct knowledge tell TMZ ... the One Direction alum was very vocal about being sober in the late spring/early summer of 2024 ... telling people in his inner circle working with him that he was on the wagon.

We're told those around him saw no warning signs of either drug or alcohol abuse at the time.

In fact, sources say Liam was often in good spirits ... even though he wasn't working on any music, nor was there a One Direction reunion on the horizon.

Liam had previously opened up about his sobriety journey in 2023, posting a YouTube video where he candidly shared he had done a 100-day stint in a rehab facility. In the video, LP noted he had been sober for nearly 6 months.

That's a strikingly different picture than the one painted by Argentinian officials, who spoke out after the singer's fatal fall from a hotel balcony Wednesday.

The Buenos Aires Security Ministry and Argentinian State Police addressed the ongoing investigation Thursday, disclosing that both clonazepam and a white powder were discovered in Liam's room at the CasaSur Palermo Hotel after the tragedy.

The white powder in question is currently being analyzed by authorities ... state police added.

Additionally, in the moments leading up to Liam's death, a hotel staffer placed an emergency call ... reporting a guest was "overwhelmed" by drugs and alcohol. There was already concern for Liam's safety, with the employee noting the staff had not been able to access the hotel room for several days.

Photos from inside Liam's hotel room showcased a chaotic scene, too ... where the television was left smashed up and other broken items were discovered on the floor.

A police official later declared the singer "had jumped from the balcony of his room." However, the investigation into the death is still ongoing.