We've had reports of this phenomenon happening to a few users. One of them emailed us back with this report:

"I just wanted to give you an update on this issue I was having. I think it has been resolved. I was looking through my Windows Event log and noticed that the SIM crashes coincided with a .NET runtime error. I ran a windows .net repair tool and now everything seems to work fine. I am even able to run in the windowed mode again and on a server without any crashes."

Run8 V3 requires DotNet 4.8 (as opposed to V2 which used 4.5), so make sure your system does indeed have 4.8 installed.