I just had the incremental update on my German Nightly fail, attaching what was in the console.

I'll also attach the update log, which at this point already is the back-up log as the complete mar applied.

Full update updated to 20190119095933.

The update log looks like something didn't get signed right?

Note, the incremental updates after that worked again, in particular the one to 20190120094340.

From the log

EXECUTE PATCH Contents/_CodeSignature/CodeResources
LoadSourceFile: destination file crc 1862124446 does not match expected crc -1624554572
LoadSourceFile fail

So, the patch for CodeResources has a crc of the file it expected to patch which didn't match the one on disk.

Hit this again on https://archive.mozilla.org/pub/firefox/nightly/partials/2019/02/2019-02-21-09-31-43-mozilla-central-l10n/firefox-mozilla-central-67.0a1-mac-de-20190220040540-20190221093143.partial.mar, final URI spec: https://archive.mozilla.org/pub/firefox/nightly/partials/2019/02/2019-02-21-09-31-43-mozilla-central-l10n/firefox-mozilla-central-67.0a1-mac-de-20190220040540-20190221093143.partial.mar

EXECUTE PATCH Contents/_CodeSignature/CodeResources
LoadSourceFile: destination file crc -389285044 does not match expected crc -1735373602
LoadSourceFile failed

execution failed

So, either the files have been modified locally so the partial can't be applied which would be the proper result or the MAR file created by releng was created for a different set of files than you have installed.

Axel, if this is still happening and you aren't modifying files locally then this is a releng bug.

I didn't have stuff modified locally. And it was happening to me twice, reported each time.

Is it still happening?

I haven't tried downloading the old builds and applying the old incremental mars. Which I couldn't do now, because the incremental mars from comment 4 are gone by now.

Likely this is similar to what we're experiencing under bug 1574404. Duplicate decision tasks for nightlies pointing at the same revision.

Likely the issue is the one described in bug 1501167.
Please re-open should you think I'm wrong.