The defendants told the judge they did not know where they lawyers were and that they were too poor to pay their own legal fees.
An official close to the case, who declined to be named, said DRC authorities had hired the defense lawyers but had not yet paid them after 16 court hearings.
The lawyers boycotted the indictment hearing in protest over lack of pay, the official explained.
Luca Attanasio, Italy's former ambassador to the DRC, was among three people killed on February 22, 2021, when a United Nations convoy was ambushed in the country's troubled east.
A military tribunal examining the murders opened in the central African country's capital Kinshasa in October. The prosecution was due to wrap up its case on Wednesday and request a sentence.
But the presiding judge postponed the indictment by one week after the defendants appeared in court without lawyers, according to an AFP reporter present.