A recent update to the 'zic' tool changed its default to "slim" mode, which will cause timelib's time and date transitions to return the wrong result. An interim solution while the full solution is being scoped is to cherry-pick the following commit from timelib that specifies a build with the "fat" mode:

https://github.com/derickr/timelib/commit/0033e3d7fa8f1bb4557842e40af66ad506f2f010