While working on a big artboard in Designer, I have noticed that rounded corners function (Corner tool) has a limitation of 168.58mm. It is possible to input e.g. 2000mm radius, the corner radius would go to 168.58mm, while displaying 2000mm in the Radius input box. Did you noticed the same? I could not find relevant info on this online. Designer persona in Publisher behaves the same, and artboard size is not a factor.
Judging from:
lacking error notification when entering Radius larger than possible,
(seemingly) arbitrarily limited size (not a rounded number of mm, feet, inches, pixels @my DPI...),
relatively smallish radius,
seeing 2000mm in the input box while dealing with 168.58mm in reality.
...this could be a bug. UX papercut for certain. My expectation is to be able to use radii at least as big as the artboard, or workspace.
I am working on the latest non-beta version, High Sierra, Mac.
Thank you!