Hi!
Sorry to bring bad news. But this usually indicates that the SL/SR Button Board ******ribbon cable is damaged at some point and need to be replaced.
Gladly, this one can be easy repaired!
Here is the guide you need: [guide|148909|Nintendo Switch Right Joy-Con SL/SR Button Board Replacement - iFixit Repair Guide|new_window=true]
Here is the part (if needed): [product|IF378-016|Nintendo Switch Joy-Con Controller SL/SR Button Boards|new_window=true]
Please let us know how it goes!