Trying to evaluate Ekos, it impressed me but i have an issue with two SBIG ccds … an ST8XME and ST2000XM. The issue is the same.
Taking a sub, every type, BIAS,LIGHT or DARK i have some horizontal band artifacts only when cooling is active. This strange phenomenon never happens when using other acquisition platforms and software based on Windows. I can exclude camera problems, it is affecting both cameras and only on Ubuntu (last version) Ekos+Kstars.
I think you should try a couple of experiments to rule out other possible causes.. You already ruled out the camera, but there are still too many sources for what the cause could be. You could connect the camera to your windows computer, run it using ASCOM and use WINDI to run an INDIServer on Windows serving up that camera for KStars. Then run KStars for Windows and connect to it and take a picture. Do you get the same banding effect? That way you can rule out another variable.
In a similar vein, you might try running the camera on Ubuntu, connecting to it with Windows KStars, and the other way around, running the Camera in ASCOM/Windi and connecting to it from Ubuntu KStars. Also, are the Ubuntu and Windows computers the same one or is it a different computer? If they are different computers, there is another variable that must be ruled out. This way hopefully you can find out whether the issue is the machine, the operating system, ASCOM vs INDI, or KStars on Ubuntu or Windows.