@John-M Typically DxPL detects any such potential clashes with items on the disk when the export starts (as you well know). I have managed to get the export clash dialogue before and effectively the images on disk passed the check when the export started but for some reason a file clash was created and then detected when the export was attempting to store the second file.
That was a long time ago, I understood what had happened at the time but cannot now remember the exact reason but a file had been created that clashed with a file being created by the time of the creation of the second file!
However, there would only be one file on disk because the attempted creation of the second file was what caused the error message. DxPL prepares to resolve such file clashes if it detects a potential clash at the start but cannot handle the problem mid processing!
@Joanna good guess but each export is treated as a separate batch and I am not sure when the “Overwrite”/“Unique” test is done, i.e. at the start of the whole process or at the start of each batch!?
PS:- I detest the “Overwrite” etc. dialogue being asked every time DxPL detects a clash at the start of an export but I think it then prepares to “overwrite” or use"Unique" in advance of the export, i.e. for the specific images clashes it detects at the start, and does not handle any new clashes except by the exception dialogue you experienced!?
@John-M Quick test started the same export twice, the second before the first had even started, and got this early on in the actual export, note the bottom right icon means that DxPL knows that another export is still due for this image (good work DxPL)