I just went through this very annoying problem with my 2600x and Fatal1ty Gaming K4, it actually doesn't have anything to do with Ryzen Master.
Step 1: Uninstall Ryzen Master, as it's not good for anything, always better to use BIOS (UEFI).
Step 2: Enter UEFI, select CPU Frequency and Voltage Change to Auto. Select CPU Frequency and Voltage Change back to Manual, the DEFAULT frequency and voltage numbers should be inputted there, LEAVE THEM ALONE, Saves Changes and Exit. Log into windows.
Step 3: By now the problem is basically solved, with the default values, frequency and voltage will go up and down on Idle and core performance boost will kick in if enabled. You can now enter UEFI and select Auto, it will work. If you run CPUZ you will see the Multiplier constantly changing.
My conclusion is that the default values on Manual work the same as Auto, if you change them, they may eventually get bugged and just switching back to Auto alone won't work. You need to enter save the default values on Manual to "reset" it.