This is not a solution, but a confirmation of a similar problem. The recent change from daylight savings has resulted in all days prior it being pushed back by a full day: Monday → Sunday; Wednesday → Tuesday; Friday → Thursday. Days after the change were not changed.
This is not quite the same as what you describe, but seems related. Is it only those before the time change affected?
Attendance (plugin)
Dates changed?
This discussion has been locked so you can no longer reply to it.