After boolean union, I lose some faces of my polysurface

balutrade_plateau.3dm (5.3 MB)

Hi, every time I try to boolean union the 2 parts of the railing, the middel part loses his top and bottom faces. Normally I would use the command ‘cap’ to solve this, but that does not work because the program still thinks it is a closed polysurface.

Is there anyone who has had this problem and knows how to solve it?

Well, after the boolean union the center part ‘disappears’ from the window – only curves show. But explode and shrinktrimmedsrf then rejoin, it becomes ‘normal’.

Thank you!