It is understood that Abba's lawyers were shocked to find his name taken off the military tribunal's list of hearings on Wednesday evening.
"I think Ahmed Abba's name has been taken off the roll, I don't know why," said Abba's lawyer Clement Nakong.
He further added that the appeal was lodged three months ago.
"International agreements that Cameroon has signed, Cameroon's constitution and the penal code all specify one should have one's case heard within a reasonable period of time."
Abba has already spent two years in jail.
Reporters Without Borders (RSF) launched a coordinated support committee ahead of Abba's appeal hearing on Thursday, to step up public and political pressure on Cameroonian authorities.
The support committee includes several regional and international NGOs that defend journalists and human rights, such as Africtivistes (a pro-democracy coalition of African cyber-activists), Amnesty International, Journalist in Danger, (JED), the International Federation of Journalists and the Committee to Protect Journalists (CPJ), which has named Abba as one of the winners of its 2017 International Press Freedom Award.
"Bringing together well-known figures from around the world and especially Africa, the committee has decided to begin online by creating a Facebook page in which we will share the messages of his supporters," said Clea Kahn-Sriber, head of RSF Africa desk.
She said the campaign would grow in strength if authorities do not free Abba.
Abba was given a ten-year jail term in April for covering the activities of the Jihadi terrorist group Boko Haram.
"Each day that RFI journalist Ahmed Abba spends behind bars in a Cameroonian jail is another travesty of justice, which sends a chilling message to the media community in Cameroon," said Committee to Protect Journalist Africa Program Coordinator Angela Quintal.
"We urge the Cameroonian government to free Abba without delay and to right this injustice. The world is watching."