Triangle sample - instable colors

[isolin]

When I run the Sample 02 with a triangle, I always get a different result. Sometimes three colors (RGB) are present, but mostly there is something missing. This changes each time I run the example without any code editing. Just a repeated dotnet run. I have the feeling that blue is always present, but red and green are often substituted by black. Any what could be the cause or how to search for it?

The correct one:

Wrong results, randomly obtained:

[isolin]

When I change the color to a single one, e.g. green then I get either all an black or all an green triangle.

[amerkoleci]

Not sure whats wrong here, never happened to me actually

[isolin]

In the cases when it messes up, there is also alpha wrong. I assume it will be some sort of a memory issue. Positions are always correct, though. And surprisingly, having a constant blue always yields a correct result.