Seems that the Samsung 840 Evo is notorious for performance degradation. : r/buildapc
Amazon.com: New A+ Samsung SSD HDD 840 PRO 2.5" 7mm 128GB MZ-7PD128BW MZ7PD128HCFV-1BW00 0Z000 SATA 3.0 6.0Gb/s MLC Hard Disk Solid State Drive Laptop : Electronics
Samsung 840 PRO 256GB for sale online | eBay
PARIS, FRANCE - AUG 3, 2018: Man hand holding Samsung 840 Pro packaging box of NVME PCIE SSD hard drive disk with high read and write speed Stock Photo - Alamy