Dualshock 2 malfunctions are usually caused by short circuits due to degradation of circuit lines, however they are easy to fix.

You can fix it by cleaning all connections and make sure the contacts are not obstructed or disfunctionals.

Make sure the flexible PCB is properly seated for having an optimal contact.

Don't forget to never force any components back together. Everything should be easy to assemble again, just be patient and you will be able to use back your controller.

A good way to test your controller is to use a USB adapter and x360ce on PC. If something is abnormal, you will notice. You will need to look at your controller again, however I fixed all my controllers with random input issues, and so should you.