Can you copy the Curtain Wall to the Clipboard, start a new Project (with settings of latest project, not based on Template) and paste the Curtain Wall in there? Is the Curtain Wall displayed incorrectly too? If it OK in the new file, there might be something wrong with your Project File.
If it still has the problem in the new file, can you put it on Dropbox as a PLA so we can look at it?
Please also include your AC version and specs in your signature.
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AMD Ryzen 1700X CPU, 48 GB RAM, Nvidia GTX 1060 6GB, 500 GB NVMe SSD
2x28" (2560x1440), WIN10 PRO ENG, AC20-AC26
Loving Archicad since 1995