New
#11
Ah @Jhawk55, so it's the High Contrast bug! Yes, I investigated that one back on 24th Oct. The bug then prevented Defender Security Centre from opening at all.
windows defender security center dosn't start correctly
Since then we've had several cumulative updates and an update to the Defender Anitimalware Client. This has at least let Defender now open, with the side-effect that my testing now shows that the only high contrast theme that it works fully with is 'High Contrast White'. It's an improvement (of sorts) I suppose
Until they fix this properly, the only workaround is to switch to 'High Contrast White' or 'None' to use the affected parts of Defender, then switch back to your preferred theme once you are done.