That happens to fillet/chamfer tool when a value that doesnt really fit for the operation is used. I went up to .2 ok, anything larger produces the funky results.

I've also found that if I need to squeeze up the size towards that limit, I can quit the command and start it again and get slightly higher results. So like for this when I created the bad chamfer with a large value, then tried to go smaller, bigger, smaller to find the limit, it stopped me at .2. When I closed the command and reselected the geometry, and then started it again and just entered .24, it chamfered well. You could also try smaller sections at a time to get larger results. Like one opening at a time.

FYI.