@jdc changed a few things and added an option in the preferences via this PR
that tackled an issue I had not so long ago (this one).
This PR also seems to fix this problem (I just tried it out).
If you run into white artefacts in your exported file(s), files are completely white after exporting or, when zooming 100+% turns them white when using CIEcam, try unticking this new option:
Preferences → Colour Management → Ciecam → Avoid Artifacts
This issue only turns up in special circumstances so it might not be a good idea to leave it turned off by default (it is actually there to avoid artefacts in general).
EDIT: Words.