I've been adding them as STL directly onto the tool. I know of the possibility of creating KRPRJ files but it's been a while since i've looked into it. loading them directly as an STL is quick and convenient.
Yes, it happens exactly when changing/rotating perspective and it also happens when zooming in and out.
My theory is the rendering process required graphically to keep up with the screen perspective changes are overflowing some internal memory/process buffering within the engine and graphics card and crashing it.
ie amount of facets/faces etc within the STL model itself or graphics incompatibility settings.
Which really Kawasaki are the only ones whom could technically qualify this or not.
Option 1:
Do you use/have you heard of BLENDER?
I use it all the time to reduce STL files when K-Roset has trouble with them and works really well.
It was recommended to me by a Kawasaki applications engineer, specifically to reduce STL file sizes not to fix issues within K-Roset.
That maybe worth a try to whilst using your existing method of adding the STL's to the Null Tool.
If you can get hold of it, I can send you a quick guide on how I adjust STL's if your interested in trying it?
Option 2:
It may just be simply your PC specs need tweaking on the graphics usage side to be made more compatible with K-Roset.
i have collision detection plugin is enabled but i'm not actively using it for this project.
Collision detection in K-Roset (as you may have experienced) slows the graphical rendering down, due to increased overheads to monitor facets on the STL models with other STL models, which could have an impact on this error IMHO if you were using it, but you are not, so eliminates that side of things.
That would be difficult without comprising IP. I can possibly send you one of the STL files for you to mount onto the robot to see if you can replicate the issue.