The code error Which[a, b, a, c] gets picked up by the plugin, but a related one like Which[a, b, c] does not. Presumably this is because CodeInspect assigns a relatively low confidence (0.55) to this case?
CodeInspect["Which[a, b, a, c]"]
CodeInspect["Which[a, b, c]"]
This is rather unfortunate, since this is a pretty important and common error to catch. I don't know what the proper solution is, but I feel like this is worth addressing.