Just an idea: those "artifacts" may be affected by the "Set Scale Factor for importing Texts and Arrowheads" options. Try to experiment with those radio buttons and see if that makes any difference. Try to set a greater scale (like 1:1000) or smaller scale (like 1:10, 1:1) to see if that makes any difference.
P.S.: I have renamed the title of the topic to a more useful "DWG conversion".
P.S. 2.: I have just noticed you posted this question 3 times in 3 different forums. Please refrain from doing that in the future, it is considered spamming. If someone knows the answer and is willing to help, they will answer to a single post.
I have deleted the other two duplicate posts in the other forums.
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