Did you put the new friction plates in dry? its a wet clutch so needs oil on the plates for them to operate properly, try wetting them with oil before starting bike up, also metal plates could be warped, you can check them on a flat surface for visible distortion, I once put a new clutch in and filled the engine with car oil because it was all I could get and the clutch did the same until I drained it , cleaned the plates off and used proper bike oil, the car oil had additives that made the plates slip because car clutches are dry, bike oil is designed for wet clutches, also tighten opposing spring bolts to equalise pressure, and operate clutch to check its function before starting up again.
Good Luck,
Jim