I’ve experienced this a few times – I go to the breaks page, there is the “Default break dates” at the top that are populated based on the current date. E.g., right now it’s Dec 27 (around noon, so no weird day-boundary edge cases should apply), and the fields are autopopulated with Jan 3=>Jan 10 (i.e., 7 days from now and 14 days from now).
When I go to set a break using these default values, I get the error message “Start date can’t be before akrasia horizon (2026-01-03)” (e.g., see screenshot), and if I change to Jan 4 then it works.
I don’t know whether Jan 3 ought to work or the default ought to be Jan 4, but I assume at least one of these is unintentional.