I also had similar problems with the carriage randomly not moving all the way on an Avantra 25, but the error was "Carriage Jam"...
I first tried to clean and re-lubricate the two rails guiding the carriage, and the problem seemed to occur less frequently, but still occured...
I finally removed the carriage from its rails and inspected its driving system, and I saw that there was a lack of link between the carriage motor and the driving wheel. Removing the carriage motor from its place allowed me to see that the "elastic" aluminium coupling between the motor and the driving wheel was loose on the motor output shaft, just because the little screw that tightened the coupling on the motor shaft was broken!
Unfortunately, Agfa uses screws with size and thread in fractions of inch (probably a 1/8" diameter), which are very difficult to find in France... So I simply removed the thread in the coupling with a 3 mm drill, made a place for a nut with a milling-machine, and installed a new 3 mm screw... and it works now (since 4 years) without any trouble.