Random soreness

Viveyp21

So I usually do the same workout every other day for two weeks before I changing it up. By the time the two weeks are up I am not sore the day after the workout meaning my body is used to it. Yesterday was the last day of the two weeks so I have done the exact same workout six times with less and less soreness each time. However, today I am more sore than I was the first time I did this circuit. Would there be a reason why this happened? Should I do the same circuit again or up it anyway?