The article mentions this 5y study (https://pubmed.ncbi.nlm.nih.gov/22966034/ https://pubmed.ncbi.nlm.nih.gov/22966034/) which included a sleep training interve

The article mentions this 5y study (https://pubmed.ncbi.nlm.nih.gov/22966034/ https://pubmed.ncbi.nlm.nih.gov/22966034/) which included a sleep training intervention at 7m, and found "no evidence of differences between intervention and control families for any outcome". It sounds like the main concern would be starting sleep training too early (sub 6 months), or using it in unusual situations where there are already attachment issues.