Sketchup faces have a white (front) and blue (back) side. If your model has a mix of front/back on the same surface, Round Corner will create a "crack."

: A cost-effective option for power users, offering 8 popular plugins (including RoundCorner and Curviloft) for Trial Period : Both extensions typically offer a 30-day full-featured free trial from the first day of use. SketchUp Community Top Free Alternatives (No Plugins Needed)

: Modeling at real-world scale for small items (like jewelry or small hardware) often causes the engine to ignore tiny edges, leaving holes.

Instead of a crack, you can obtain a legitimate perpetual license for a low cost through SketchUcation .

Searching for a "crack" for SketchUp extensions like RoundCorner