well...
I think explorer itself sends the fileaction command to each file, so you can't directly fix it.
but you could make your script have a wait a second thing.

like, the first file gets to the script, it writes it to temp ini file.
then, it waits a sec or so waiting if more files appear.
the other files are also triggered similarly so they also add to the ini.
if they see the other process running, they quit there.

this leaves only 1 process that processes all of the files.
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