MultipolygonsZ and MultilinesZ (lines and polygons with Z values) make the generation of forest roads fail.

[Klemet]

Issue discovered by talking with a user by email. Noting it here for future reference.

The QGIS functions used by the plugin seem to fail when using the special type of "MultipolygonZ" or "MultilineZ", a special type of geometry where each point has a third "Z" coordinate related to elevation. When this is provided as the "Roads to reach" or the "Polygons to reach" layer in the algorithm to generate forest road, the algorithm will fail and say that "no roads/polygons are in the raster".

To make sure of the type of geometry used in your layer, double click on it in the layer menu of QGIS.

If it is a MultipolygonZ or MultinlineZ, just transform it into regular polygon/lines with the "Drop M/Z values" tool of the processing toolbox of QGIS. Then, try the algorithm again with the regular version of your layers.