Odd print artifacts on same layer as large top surface
Just a guess here. If I understood correctly the deformation is at the first layer of the box bottom, it seems highly unlikely that it randomly happened at this exact position so I am assuming that if you do the print again you will get the same deformation at the same place (you can test this maybe ? I know it is a long print). In this case it is more likely that is a slicer issue than something with your machine and it could also be a problem with the stl model. Maybe try to create a small simple box then slice it using the same setting and try to see if you can reproduce artifact.