I dunno, if that's just on light load then that just sounds like a mounting/mounting pressure/contact issue. Especially if it's idling at 50C, without any noticeable background tasks going on. Ryzen idle is pretty annoying but it's easy to tell when it's actually idling and when it's running something in the background. New Be Quiet mounts on the DRP4 are an improvement but sometimes take a bit of fiddling compared to Secufirm.
I don't imagine the similarly sized Shadow Rock LP performs much worse than the NH-L12S, which is stout as hell and kept my 4650G at less than 65C at all times during the short time I had it. Renoir is slightly cooler but not by much. My NH-L9x65 now keeps the 4650G at under 70C at all times, I figure between Matisse and Renoir add about 10C to account for chiplets.
When I had my 3700X it crept closer to 80C under all-out CPU benchmarks under my NH-D9L, which is worse than my NH-U9S and performs about the same as the NH-L12S. IIRC the 3600 doesn't really run any cooler than the 3700X because it runs more wattage per core, and still takes up the 88W PPT and doesn't really "save" any PPT unlike the 5600X.
The 2019 Low-Profile Cooler Shootout: Crowning a Welterweight Champ | The Tech Buyer's Guru (techbuyersguru.com)
An all-core under 1.3V between 4.0-4.2GHz probably works out best for everyday thermals, but make sure it's not a mounting issue first.