First check J_1IPART1 table whether the Part 1 is already updated for the Material document. If not, please try to display the J1IEX and see whether Part1 and Part 2 are appearing at Item and Header level respectively.
You can update Part1 if it is not already updated. Use J1I5 and Input Material document number and other details like Posting Period, register type, posting date, Excise group, Plant and execute it.