https://www.marcospecialties.com/pinball-parts/03-8614 This is the belt to use, always amongst the first things to change when reel as issues. You can test if the optos turn on by watching them through a mobile phone's camera. If they light up they will glow purple on screen. Also verify the connections of all wires of the optos. Its very possible you have cracked solder joints on either end of the connections.
A vast majority of reel issues are fixed with the correct belt.