I came across this issue when trying to use simplify on a polygon layer. Simplify stops because of invalid geometry (Example of problem spots).
When I try to check the geometry using the available tool (check validity), the whole polygon gets labelled invalid, and the areas indicated in the picture (Example of problem spots) are highlighted as errors.
I attempted to remove these areas by using delete holes, but this only fixes the errors inside the polygon and not those around the edges.
How can these be fixed in a methodical, automated way? I get hundreds of such errors along the edges of the polygon, and this process will eventually have to be repeated for hundreds of other shapefiles, so a manual approach is not feasible.
Background: I am using QGIS 3.2.3 - Bonn, and I have limited experience with the software and GIS in general. I did not generate the original polygons myself, so I don't have control over that unfortunately.
