I heard about a similar issue. The controller was recording a movement of a thumbstick every time a L2/R2 was pressed. [br]
The problem was the wear of a sensor responsible for moving up and down of the analog stick. The solution was installing a new sensor. [br]
I saw a few videos where people tried to clean the sensors with IPA, but it was a short time solution, and the issue came back after some time.[br]
I would suggest you to try replacing the analog stick mechanism on your own (if you have any experience with using a soldering iron). That's not as hard as you may think :)