As such, the general bias against publishing non-significant results could mean the conditions for being able to even try such a review risk biasing the review towards exaggerating agreement.
(It also seems the Cochrane review here may itself only be considering other reviews - a metameta analysis of sorts – which might also be influenced by a selection bias, if there’s any chance at all that researchers choosing work, & then publication decisions, prefer to address questions where there’s more agreement, rather than less-attention-catching mixed results.)
The most convincing evidence here would be how strongly preregistered RCT results, whether ever published or not, tend to match earlier observational studies. It doesn’t appear to me that this Cochrane review is focused on that.