Sorry that you hit this issue. Can you tell us which version of JMP you are using?
Windows paths have an historical limit of 260 characters for the full path. It's possible that the OS APIs we're using are truncating things and the only fix there is a shorter overall path as was suggested. Or, there could be a bug in Files In Directory.
Do you know the length of the full parent path down to the problematic folder? If that length (including the drive and \ chars) + the 134 of the directory you are enumerating goes over 260, the names will get truncated from the OS.
Since you may wonder: We do have a wish list item to support long file names in the future but that is quite complicated as the long paths are structured differently than normal paths. They are prefixed with \\?\, for example. Also, there is a LOT of code which deals with files which would need to be rewritten. Supporting long names would also require you to edit the registry to enable it the machine.