I upgraded from a GTX 750ti 4GB to a 1660ti 6GB and suddenly, a weird behavior with V-sync started happening, not only in Retroarch, but with other emulators and games too. With the GTX 750ti I had constant 60FPS without any issue with every core I played, now it drops like this, goes down to 58, 59 and 60, then again and again, but basically stuck on 58 causing micro stutters. The only thing I changed from the GPU upgrade was a driver update. Settings on Nvidia Control Panel are the same, Power Management set to Prefer Max Performance, V-Sync On.
Edit, I fixed it by reinserting the GPU and making sure everything else was clean and fit.