I have encountered a similar situation. I think you should only include the study that involved the full data set

It sounds to me like you have two reports of the same study (i.e., one study, not two); each report, however, is incomplete. The "study" is the unit of interest in a meta-analysis. It is perfectly fine to combine results from the two reports. Of course, you have to be careful not to duplicate data.

Just ensure that you will use non-overlapping data from both studies of the same sample, and explain this in your results and discussion. Otherwise, haphazardly using all data from both studies will clearly lead to duplication (i.e., the "weight" of the sample observations being doubled compared to other included studies that do not have the same issue).

You need to account for the dependency between these two studies. Given that the subjects are the same, the assumption of independence is violated. The best way to do that is with a multilevel analysis. More explanations here: https://bookdown.org/MathiasHarrer/Doing_Meta_Analysis_in_R/mlma.html