Sync frequency for the Modbus register in that case is very important for a smooth movement,
movel, movej or similar script movements work just as a standard Move commands and waypoints.
The original position is moved along with the conveyor by the conveyors speed.
servoj is used for online control, and hence the positions are expected to be updated at a given update frequency.
So servoj might not give you the expected behavior inside conveyor tracking.