Chamfer makes my object disappear (newbie)

[tzulah]

I'm brand new to FreeCAD and pretty new to modeling in general (but I am very determined).

I am trying to create a series of stamps. Each stamp will have a unique shape embossed into it. I have figured out how to import my svg shapes and extrude them, and punch them out of a cylindrical slab. I even figured out how to center align them to each other (that was harder than I expected).

What I can't figure out now is how to bevel the edges of the inner shapes (this is a necessary requirement for the working stamp. I have tried them without it and it doesn't work). I have done several tests, and I can get a simple ring to chamfer nicely, but when I try to chamfer one of my actual shapes the whole thing disappears. I have done quite a lot of looking around for help before posting here, but so far I can't figure it out. I did "Check geometry" and it was ok, and I've tried a variety of chamfer edge lengths to no avail.

I'm attaching a picture of a very simple test shape (note that this shape is just a simple outline - many of my actual shapes have inner sections also (such as letters of the alphabet).

Can anyone point me in the right direction? I'm sorry to say that I have put dozens of hours into different methods of making these stamps and learning different software tools, and I feel so close now but I'm still thwarted. I've had lots of success modeling other things but these stamps are just not working. I will be eternally grateful to anyone who can help me make this happen.