hi,
do not use account assignment in your process when you need to stock the material, Account assignment categories mainly used for procurement of consumables.
You are using account assignment 'F' which directly posted to consumption account when you do GR,
do the process without specifying the account assignment & check the stock in MMBE,
Please revert your business requirement clearly, do you have any specific requirement to use account assignment in process?
Thanks,
K J