The one trick you can try is to change the Version number for the customization. Export the customization to a .CST file. Open in Notepad or Notepad++. At the top of the file, you will find a file header that looks something like this:
' Begin Customization Screen: 0101000 Version: 5 Sequence: 300 Description: "A New All Users Customization" System Administrator: FALSE Secure: 55
Change the Version: 5 to 6, then save the file as a new .cst file. Try importing the customization back into SL and see if that helps.
The other thing that may have to be reviewed is if there is any custom code in the screen that required importing a .DH file. If so, it is possible that the schema for the table as changed, and will need to be updated with the current .DH file from the SL 2018 version.