How often does it happened? Is it in the same circumstances? (e.g. 5 sec after you open AutoCAD) I have the same problems with mine but only when I wake up the computer from sleep. Though mine is OK in any test try to benchmark yours. If it crashes I believe you can safely assume it is the GPU. Even if is OK you can still buy a graphic card, replace yours and if it does it the same you can always return it if not problem solved.
Samsung Galaxy S9 review