Python script cannot find file only sometimes

Question

I am running a Python script multiple times and the only thing that changes each time is the name of my run.

Approximately 50% of the time, the runs fail and I get the error output:

IOError: Cannot find file filename.txt

But the file is certainly in that location when I check. And the same file is also used by all the other runs that succeed.

So I'm just trying to understand what if there is anything that could be producing this error only sometimes.

I don't know if it's relevant but I am submitting the jobs via Slurm on a remote machine.