CJ20N material cannot Reservation for WBS

Hello friends,

while We put material in project builder CJ20N, chose procurement type is Y1( reservation WBS element), and use item category is L( stock item).but WBS element column shown blank, and procurement type shown reservation for network.

it is wrong ,

we need the materials should be reservation for WBS. meanwhile we found grouping WBS element shown gray, cannot edit.

Could you help us to analyze the root cause and give the solution. thank you.

regards

Grace