I think a lot of people don't take the ambient room temp changes in the room into consideration with cloning. In winter vs summer my house will vary 20 ish degrees. That 20 degrees makes a huge difference in cloning. So when people do the same thing every time and seasons change, results will vary.
Like dr running his pump 24/7. It works now, but it doesn't mean it's gonna work in the summer. I only just picked up a heating mat like a year ago cuz coincidentally most of my cloning fails happened in the winter. Given we all live in such varying environments it makes it nearly impossible to follow someone's setup and get the same results unless they're your neighbor.
Kinda related, my sister is growing SRS and in flower and were developing really slowly. She sends me pics and I don't get to see it in person much. So anyway she's running the same plant, same temps, same soil and nutrient line as me but her shit looked 2-3 weeks behind. I first thought light leak, and went through ruling that out. Didn't seem to help.
When I was able to get over there I found that although the air temps were good, she was using smart pots right on the concrete and the concrete was freezing ass cold. Got them off the ground and everything was gravy.
Variables, variables.