For the last several days (perhaps about the time Dark Mode was introduced?) I’ve noticed that the “tool tip” text I see when hovering over the contribution “histogram” (the green bar with a square for each day in last year) is off by a day.
For today (Dec 17, 2020) it says “1 contribution on Dec 16, 2020”.
As near as I can tell everything else is correct, it is just the tool tip that is off by a day. In case this is a time zone issue I live in California (PST, UTC -8).