It looks like a rootzone pH issue, low temps, and/or too small of pots. It could be due to a recent transplant, but at 3wks I’d think they would have figured it out if it was just transplant stress. Could also be temps (too cold) or too much light. Definitely increase the temps if they’re under 80F during the day or 65F at night- they really enjoy tropical environments.
If I had to guess, I’d say high pH and cool temps because I think you said you were using big pots? The soil company recommends 40L minimum per pot. That soil has lime in it, which raises pH. You might check your water to see if it’s also high out of the tap. If so, pH’s likely the issue. But that’s just a first guess.
The soil company also says you should topdress with their organic amendments, so I don’t know if maybe the soil isn’t very heavily fertilized and it needs more juice for them? It’s hard to say without knowing how much of the ingredients they put in there.
Hope that helps!