Coz Part Design crashes on those sketches. Does it crash for you?
Why would it? If i can change sweep curve radius to 4mm, do sweep, change it back to 3mm, and it magically works. But it can't, for some reason, do the sweep with the original 3mm curvature radius directly, without the intermediate 4mm step.
I don't even know what "raduis = 0 or negative" you are talking about.
The internal cylindrical face degrades to a line. Because of rounding errors/number representation/sketch solver precision/... this line could sometimes still be interpreted as a face and ócasionally work. If the sweep profile in inside more than the bend radius this creates selfintersecting surface which should not be valid. Checking geometry with 2.9mm bend radius gives a lot of errors - the "-0.1" radius.