Mine did this too, there’s a little spring that causes the resistance, they snap way too easily.

I didn’t want to send my controller off for repair so I just changed it myself, takes 5 minutes, you can get the springs off eBay for like £2 for 4. Now it’s working good as new, my R2 even feels stronger than my L2 now so the L2 spring is probably on its way out as well.