In part it is because your software is not turning the gears at the correct ratio. Maybe you are not correctly adding/subtracting the angle the carrier turns from the angle the planet gear needs to turn to keep correctly meshed with the sun gear.
For each clock-wise turn of the carrier, the planet will make 1 turn clock-wise + 30/9 turns counter-clockwise.
Do you want to know why the gears in your cad simulation do not seem to be synchronized in rotation? Or do you want to know why there is interference between the gear tooth profiles as they pass in/out of mesh?
With regards to the latter, your epicyclic with a 12T sun, 9T planet and 30T ring requires a fair bit of tweaking to simply mesh without interference. Getting the gearset to mesh "smoothly" will be a far more difficult task.
