Hi LM, the object you posted will Chamfer ok if you select the entire object instead of only some of the edges:





It's a lot more difficult to chamfer or fillet only some of the edges that come to a shared vertex instead of all of them. That's because the fillet surfaces have to be extended and intersected against each other in that situation instead of being able to make a corner juncture patch.

In your last screenshot the issue is probably the distance you're using is too large to fit within the available area.

- Michael