I am also facing the same issue. I have a website with the name of www.classykart.in built on minimal theme.
I am trying to upload a CSV file for COD serviceable pincodes codes but it is saying processing & it is sitting on the same screen from several hours. List has around 25000 pin codes, I have tried entering pin codes manually , If worked fine for a fewer pin codes but as soon as I entered all those 25000 pin codes manually it just crashed. It keeps on happening everytime.
Screenshot of uploading CSV shared for reference. It is sitting on the same screen for hours.