2 possible things.
Windows missreport -> check with something reputable. (make sure to check temps also, it might be thermal throtling as you could just make a mistake while mounting)
missconfiguration or apparent missconfig.
1.2Ghz seems like minimal speed so check power plans for minimal and maximal cpu speed. A how to:
https://www.tenforums.com/tutorials/2843-change-power-plan-settings-windows-10-a.html
you want to set minimal lower than 30% and maximal 100%.
if you set minimal high, cpu will not have time to cool down, if you move max lower, you will get less heat and less performance (good for laptops)
you might want to go to bios and reset to defaults, it sometimes helps.