x1c reporting clogged nozzle

anyone know how to fix this.

took extruder apart several times and its always clean inside , no debris, i also changed the nozzle.

if i turn the printer off and on again it will print with no intervention but if its multi colour it will say extruder clog at filament change.

ive tried googling chat gpt and bambu wiki with no joy.

thanks in advance for any advice or tips to solve this