Strange.
I could reproduce this bug easily with AC13 too.
ArchiCAD cannot do a full circular Wall as one element so if breaks it up into two Walls. I think that fact that the two half-circle Walls join at the same point as the inner Wall has something to do with it.
Workaround: If you rotate the two Walls, let's say 90 degrees so the point they join does not coincide with where the third wall joins them, there will not be a problem.
I will report this to GS.
Loving Archicad since 1995 - Find Archicad Tips at x.com/laszlonagy
AMD Ryzen9 5900X CPU, 64 GB RAM 3600 MHz, Nvidia GTX 1060 6GB, 500 GB NVMe SSD
2x28" (2560x1440), Windows 10 PRO ENG, Ac20-Ac27