UltiMaker uses functional, analytical and tracking cookies. Tracking cookies enhance your experience on our website and may also collect your personal data outside of Ultimaker websites. If you agree with the use of tracking cookies, click “I agree, continue browsing”. You can withdraw your consent at any time. If you do not consent with the use of tracking cookies, click “Refuse”. You can find more information about cookies on our Privacy and Cookie Policy page.
The grey area appears to be related to print options, like skirts and brims and so forth - and somewhere in that mess of code there's an "out by 1" error, or someone accidentally put ">0" when they mean ">=0" or whatever, causing the full build volume to be unavailable.
Changing the size of the build area in the printer profile to make it larger than it really is, ended up working OK. Lucky for me, the firmware seems happy to let me print past the maximum extents allowed - so I guess as long as the print head doesn't hit an end-stop, that's your *real* printable size... on the chiron.