I have a new 10 speed grx group set. The right hand shifter have only 9 gear. I check the problem is in lever,i felt in high gear it was making a big jump. Are there any suggestions for someone who is having a similar problem??
@ArgentiApparatus is correct - 9 clicks is 10 speeds. Your lever starts at one end, in a gear position, and the first click puts it into the second position. Thus there is one fewer click than gear positions.
You definitely have a 10 speed shifter, confirmed by https://bike.shimano.com/en-EU/product/component/grx-10-speed/ST-RX400-R.html
There remains the possibility that the shifter is somehow faulty, or that your indexing is not correct.