new sandisk extreme 1TB very slow

i am using my new Sandisk Portable Extreme 1TB with original USB C to USB C cable and the data transfer is very slow - around 40mbps and drops to 20mbps. It is supposed to support upto 1000 MBPS. i am using a dell xps 7390 with 512 GB SSD.
Any ideas why its so slow ?

Hi @dbsandisk ,

Have you opened a Support Case? If not opened, for more information, please contact the SD Technical Support team for best assistance and troubleshooting:
https://kb.sandisk.com/app/ask