I thawed my SH-SY5Y cells in DMEM with 50%FBS in T25. The cell morphology after thawed for 24 hours look good and I changed medium with DMEM with 50%FBS. I maintain the cell until it reaches confluence to subculture then subculture to T75 in DMEM with 20%FBS( the cell will be culture in DMEM with 20%FBS for two passages then the cell will be culture in DMEM with 10%FBS). I normally use this protocol but recently I got problem. After I subculture the cell from T25 to T75 some of cell not attached to the flask surface and after I keep cultured the cell the confluence is decrease.

Do you have any suggestions ?