Ground Clutter setting seems to be the issue here.
Go to C:\Users\YOUR_USERNAME\Documents\My Games\Kitten Space Agency\settings.toml and change:
groundClutter = true
to
groundClutter = false
Solved for me. Issue happened even for Earth Only system.
Did run KSA on RX6600 quite successfully. Had to terminate all the rest processes which were consuming VRAM, so I managed to run Solar System with 4k Vessel textures and shadows, 4k shadows and 8k textures for Surface (or whatever second thing is named).
Also made benchmarking, and KSA already...
Ga.e requires at least 4 GB, but you must clean everything else to fit the game. I used Process Hacker 2, so I could terminate other processes which were consuming VRAM.
Could only fit 1k shadows and textures (system texture 512) with Earth Only in 4gb.
Also confirm, that issue is fixed once you disable AA or switch it to MSAA 4x. Issue returns if you switch AA back to MSAA 2x from disabled state.
OS: Windows 10 22H2
GPU: AMD Radeon RX 6600
GPU Driver Ver: 32.0.21033.2001
CPU: AMD Ryzen 5 2600
RAM: 16GB DDR4
Build: ksa_v2025.11.4.2791