OK, this was very odd. The script was working with aliases. An alias to a file (generated from an Entire Contents ASObjC command) copied to a directory on a remove volume.
The script was working in a directory with 1800+ files. It would process about 50 files, then generate that error for every file after.
I switched it to System Events and same error. I switched it back to finder and the errors went away.
No other changes to the script (and I verified that the correct number of files were copied)
All that said, I had been trying to run an SD log in order to see the results, etc. But it seems the log no longer has the option to generate the output in a form like Script Editor anymore. Instead of the log telling the story of which events are sent and what the results are, I get these encapsulated lines with little information.
I very rarely use the logs, so it may have been this way for a long time.
I prefer the SE log. In fact I pasted the script into SE and ran it from there just for the logs.