There haven't been any important changes within months beside aarch64 stuff & an improved gaussian audio filter.
If you re-run the game does it slow down at the same spots everytime? If not I suspect your device is thermal throtteling Which games do you run? I've tested PCSX reARMed with Gran Turismo 2 with enhanced resolution and it ran fine for me.
Otherwise delete retroarch.cfg & retroarch-core-options.cfg to get rid of old configurations.
Thanks again for getting back to me. I rolled back to the RC5 or RC4 build and it works flawlessly on all games (I tested with Metal Gear Solid). Once I update to the latest RC and official builds, the music begins to stutter right away at the "Konami" intro screen and the rest of it is choppy and slow. All I did was drop the .tar file in the .update folder and reboot. Not sure why this would cause anything to change on my config files. I'll do some more testing on my end once I find the time. Rolling back seems to allow me to enjoy my games anyway.