I remember a strange issue with copy-pasting several years ago.
It turned out it was somehow related to Word.
What I did to solve it was I went to Word, typed a few characters, then selected them, pressed CTRL+C to copy them to Clipboard, pressed CTRL+V to immediately paste them back into the Word document, and after I did this strange ritual, the copy-paste speed in ARCHICAD returned to normal.
I don't even know how I managed to figure out this solution at the time, but it worked. You can try it, maybe it will help you.
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Loving Archicad since 1995