If the Excel using macro or Power Query with "auto-refresh mode from external sources" after file open, most probably JMP cannot read it directly through JSL. I think the logic is "Excel is refreshing ..... ~" & JMP is not a software to "Refresh Excel" .
In my case, I still can open it manually in JMP.
Out of curiosity, does "file updates automatically" means the original raw data updated or "cleaned data which has gone through some clean-up/calculation automation in Excel"?