Fluctuating clock speed is normal operation. Don't use CPU-Z to monitor sensor behavior. Download and use HWinfo.
Never use CPU-Z, Open hardware monitor OR HWmonitor. They are all grossly inaccurate on certain chipsets or with some specific sensors. Overall, they are junk programs mostly. Use HWinfo or CoreTemp.
CoreTemp is great for just CPU thermals. HWinfo is great for pretty much EVERYTHING else, including CPU thermals, core loads, core temps, package temps, GPU sensors, HDD and SSD sensors, motherboard chipset and VRM sensor, all of it. Always select the "Sensors only" option when running HWinfo.
In order to help you, it's often necessary to SEE what's going on, in the event one of us can pick something out that seems out of place, or other indicators that just can't be communicated via a text only post. In these cases, posting an image of the HWinfo sensors or something else can be extremely helpful. Here's how:
*How to post images in Tom's hardware forums
Run HWinfo and look at system voltages and other sensor readings.
Monitoring temperatures, core speeds, voltages, clock ratios and other reported sensor data can often help to pick out an issue right off the bat. HWinfo is a good way to get that data and in my experience tends to be more accurate than some of the other utilities available. CPU-Z, GPU-Z and Core Temp all have their uses but HWinfo tends to have it all laid out in a more convenient fashion so you can usually see what one sensor is reporting while looking at another instead of having to flip through various tabs that have specific groupings.
After installation, run the utility and when asked, choose "sensors only". The other window options have some use but in most cases everything you need will be located in the sensors window. If you're taking screenshots to post for troubleshooting, it will most likely require taking three screenshots and scrolling down the sensors window between screenshots in order to capture them all.
*Download HWinfo
For temperature monitoring only, I feel Core Temp is the most accurate and also offers a quick visual reference for core speed, load and CPU voltage:
*Download Core Temp
Also, check your bios version and then compare it to what the currently available version is on the motherboard product page. If you do not have the most recent version installed I would update. All of the Ryzen boards have had serious firmware issues regarding CPU behavior and memory compatibility, as well as some GPU card compatibility concerns. Newer bios address these issues and should be updated to.