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Core's Nightly Jobs and Retention Policy is calculated using UTC time. When DST change is happening, it will skew the start of nightly jobs 1 hour earlier or later, depending on when the Nightly Jobs were configured originally.
To workaround the issue, Nightly Jobs time need to be changed manually right after DST change is in effect. To access that setting, please click on the Settings in the Core console (gearbox icon) and scroll down to Nightly Jobs, then click on Change icon next to the Nightly Jobs title.