That is the PBO (Precision Boost Overdive), which is similar to Turbo Boost on Intel CPUs, kicking in.
It boosts the clock speed on 1, 2 or more cores as needed when the CPU is under load.
I would leave it on as it is a good feature that will definitely improve performance with no negative effects that I know of.
I have a Ryzen 5 2600 OC'd to 3.95 GHz which gets me close to the stock performance of your 2600x.
If I had a 2600x I would leave it at stock settings with PBO enabled.
Run Prime95 torture test. Guaranteed you'll get all those cores running at 3.6GHz (assuming your cooling is sufficient). At loads of less than 100%, the cpu will assume it can go faster on a few cores, as faster = better. As long as the cpu temps are not in throttle ranges, the cores will go as fast as they can, which in your case is 4.1GHz.
This is a benefit. There's not all that many games or even programs that will max out 6c/12t usage, they'll generally use 4c/8t at most, so bumping speeds with PBO gets higher performance on fewer cores.