Which Scout function options are you using?
When computing connectivity at the Scout level, there must be a dimension reduction from sources to scouts. This reduction is called in Brainstorm "Scout function" and it can happen before the computation of the connectivity metric, or after its computations. Consider these cases of computing wPLI for a Scout and itself.
If the Scout function is applied before, wPLI must be 0 for the Scout and itself, as time series in the scout sources are aggregated, and then wPLI is computed.
However, if after is selected, wPLI is computed for all the combinations of time series in the scout sources, then, the Scout wPLI is computed aggregating all the other wPLI. So it is not guarantee that wPLI will be 0.
Check this link for further documentation in the Scout-level connectivity:
https://neuroimage.usc.edu/brainstorm/Tutorials/CorticomuscularCoherence#Coherence_Scouts_x_Scouts