Train doors at Front M2 car were not proven closed. TC opened and closed a few times to no avail. Staff (CCK) assisted in isolating Rear M2 car "A4" door for train to depart. ~~~~~ Downloaded ER and confirmed FC-083, A4 door operation time out. CLE 805 2669 occurred and cleared. Checked J-rail, Door gauge rail, Door post weather strips, no FOD found. Door mating strip 63.1mm. Checked DCS and actuating plate - ok. DLS rigging ok. Door push/pull-6.4kgf. Door opening/closing within criteria. Door cyclic test x10 times - ok. Checked by Lincoln Koh. 31/05/21.