Vadim,
it looks like it's just a matter of your settings.
1) first of all - look at the configured block for adding goods in the process. Check all the ticks
https://take.ms/qskvU2) questions about the product. you show the suppliers tab on the screen, but the price is taken from the product card, and the price is substituted there according to the settings and rules
3) in the process, apparently, the client who can have a discount is indicated. Also, the discount can be stated separately in the list of process goods.
check again and write back what happened.