Hello,
We cannot see your Shiny UI code, but does the user have to upload 4 different files before you want them to be processed? If that's the case, you can create a button that says: "Create plots now" or something and put all the logic for generating plots in there so it's only executed once when the button is clicked.
If this is not the case, try to create a Shiny Reprex. Shiny debugging and reprex guide
Good luck,
PJ