If I am understanding correctly, this 'hysteresis' effect could also be caused by tiny bits of iron contamination in the sample?
Complex answer: Maybe. Copper sulfide does a lot of weird things, and it's very easy to screw with ferromagnetism in unexpected ways. It's totally possible there's a lot of iron in this sample, and the huge incentive for room temperature superconductors is a powerful temptation to slant your data... or fabricate it entirely: https://www.science.org/content/article/plagiarism-allegatio...
That's my alma mater :(
Examples from that page put through Google Translate:
"Submitted by: Guided by the big assembly, with really cute stupid, wash the teacher,Sekiyama Pass, Fire Machine Immortal, Frog, Teacher Chen, etc"
"The rivers and lakes are far away, and I still remember that the cute and stupid sent the statement of "don't do it, whoever likes to do it" several times, and began to return to the old business in a few days. Don't say it, I really believed it at the time. Only the scumbag told me, impossible, absolutely impossible, he burned dozens of furnaces, much more fierce than us."