Minimize radius at recess edges

Hello,
In my current project, I am modeling a pane element in Sofiplus-X with several triangular openings. To avoid large stress peaks, the corners are rounded. However, I have noticed that I cannot reduce the rounding radius by more than 2 cm; otherwise, the following error messages appear: (333) “Edge curves of structural surface (SAR) 1018 are incorrect,” and (331) “Edge edges of structural surface (SAR) 1018 are not closed.” I previously created the triangles as a polyline in Sofiplus-X. Does anyone have tips on which setting I need to change to prevent these errors?