SanDisk Extreme Pro 128GB becoming very slow

The advanced bios menus and setup options Kisianik.

supports fast charging of usb connected devices such as a phone ect via a cable by default are turned off in the bios and have to be enabled.

Plus formatting of the drive and the type of format does matter and effects the final speed result .
Daft as it sounds but usb super speed if the option for it exists in the motherboard bios is enabled.
Or any 3.0 or 3.1 device compatibility is enabled.