hi, i’m following a tutorial on Sub-D, it requires that i bevel that loop but it fails i do not know why, any help? thanks 
Dear @antonio.espositocod your geometry is mirrored with reflect - the light gray (left in the video) part is the reference part, the dark gray (right in the video) part is the reflected “clone”…
you should edit the left / reference part of the object - try the same workflow on the other side.
does this solve your probleme ? mark this post as solution.
hope that helps, kind regards -tom
thankssss!!!