I am trying to do the operation "Join attributes by location" in QGIS. I have a point layer and a few polygon layers, all of them in shapefile format. I want to sum the values of the attributes of the points inside each polygon, and add that sum as a new field in the output polygon layer. The problem is that in the output polygon layer, several of the polygons from the input layer have gotten lost in the process. Why could this be?
This problem happens with some polygon layers, but not with others. And for one polygon layer, still, the operation worked fine on one computer, but not on three others.