VeraCrypt not working correctly on M.2 Samsung 960 Pro



I am disappointed from properties of VeraCrypt which I have chosen to use on my new PC on disk Samsung 960 Pro 512 GB that has transfer speeds of 3500MB/s read and 2100MB/s write. After encrypting the drive on Windows 10 the speed dropped rapidly only to 550 MB/s read and 1000 MB/s write even though I used AES method where VeraCrypt tells me it can do 7.7 GB/s. The mentioned drive was very expensive and encryption is mandatory for me so I'm asking if my money for this super fast Samsung drive went to waste? Do you have any solution? Thank you for your reply.