Okay, I have been able to narrow this down in our project but still have no solution so I will be contacting Opto22 support.
Most of our screens are the full resolution of our monitor. On one smaller window there is one element that uses a Control Engine Driven Attribute > Visibility/Blink (Discrete Trigger, Med. Blink when ON, Invisible when OFF). When that element is ON / blinking we occasionally get a similar sized artifact in the larger (full screen) window behind it at exactly the same x / y window position as where the blinking element is located in its own window.
All our windows are set to “always in memory” and it is interesting to note that once this smaller window has been opened, we can close this window and as long as the Control Engine Driven Attribute that causes the blinking on this small window is still active, we continue to see the artifacts appearing on the currently open (full screen) window.
The other interesting thing is that the issues seem to occur more or less often on different hardware platforms indicating that it may be linked to system performance.