this is the reason I spend money on good products. like Samsung 970 980 pro if possible or Crucial mx 500 ... etc ... etc ... some hardware are sata\nvne depended on needs
when i was upgrading pc few months ago bought 1tb nv2 to install windows on it. Month later pulled it out and threw into trash and bought kc3000, this one works alright. kc3000 wasnt really upgrade from sata ssd as windows doesnt boot faster or do things i do faster. i think I'm going to pull these nv2 2tb ones too theyre still 100% and will replace them with something else likely sata ssds as theyre more reliable. On sata ssds i was always getting 500mb/s no matter how big files i was copying. problem with nvmes is that doesnt matter what you buy even best one will struggle if you want to copy 100gb folders filled with small files from one drive to other the speed will go to mb/s
if your SSD is crap & almost full & is type of dram-less it can also cause such things more + A + B+ C EQU more slower
got one sata ssd Samsung 870 evo use it to test things, dont even know if its dramless or not but never whenever copied to it or from it speed never dropped below 500mb/s and second sata is Sandisk old ssd bought it like 10 years ago or something use it to test things it was really abused drive theres still 90% life left in it and the same whenever copied to it or from it never dropped below 500mb/s when i first bought nvme i was like man look at this lol so small then i saw explorer freezing, temp around 60C yeah Kingston nv2 500gb.