I’ve built the rig following Essential Blender for a character and have encountered a problem while weight painting. The lower leg bones have produced very strange results when painted - the mesh scrunches up and almost disappears (only happens on the lower leg bones). This problem appeared when I first assigned the armature to the mesh as a modifier.
ETA I did improve the situation a little by making sure that none of the controller bones had Deform turned on. There’s still a problem at the knee though, despite quite a bit of geometry there (3 loops at the knee plus loops further up and down the leg).