It is hard to reflect to what you are saying if you are using AC18 as your signature states.
Performance improvements and optimizations are continually happening in newer and newer ARCHICAD versions, including the just announced ARCHICAD 22.
Is this issue in AC18 or AC21, maybe?
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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