The AGESA ComboAM4v2 126.96.36.199 BIOS update is causing issues for CPU performance and OC ability.
People have been reporting a lot of problems after the latest update to AGESA ComboAM4v2 188.8.131.52 is AMD’s new firmware. This update cannot be rolled back so if you are thinking about doing this update, think again. A few manufacturers also decided not to push the update as the problems have been reported many times online after users experienced problems after the update. Issues are mostly related to “tanking performance”.
Some users have experienced a drop of up to 100MHz for single core clocks and 150MHz for the ones with multi cores.
There are also issues occurring with the low fabric clock (FCLK)/memory clock ratio, suggesting that the firmware is causing everything to fall out of sync. The ability to change up the ratio can be great for overclocking purposes, but not so good if it’s fluctuating all by itself. (Source)