I have some problems with my renders when rendering high res.
I testrendered brakes and rims earlier at 3000*2000px and it worked fine, but when I rendered at 4900*something px the mesh gets blotchy with black spotslike marks. The spots are different size depending on min max values in irr map.
Can you show a part of that image? You can try to render the irradiance map at lower resolution and then use the saved map and see if that fixes it.
Best regards,
Vlado
No I can´t show you anything yet, sorry. But I´ve worked with this some more and if I import the geometry that is blotchy the first render is fine, and sometimes the second, but then it gets blotchy and I need to reimport the geometry, very annoying 
It workes fine when I´m not using GI.
The geometry is CAD data importet and exported to max via maya.
Cad data can sometimes bring in things like duplicate faces and so on - it might be an error in the mesh? We’d really need to see a small portion of the render showing the problem and we’d normally be able to tell what’s causing it.
Is the irrmap mode set to “incremental add” instead of “single frame”, that would make splotches build up.