this seems to be an oversight on our end when we switched the export flow to maya only (whereas we used to use 3ds max for weapons during development). Maya seems to behave differently when it comes to the naming and turns it into filepaths. So having the same "Dummy_FX" name in multiple layers causes conflicts in the rig lookup we're currently using.
While we're taking a look at solving this issue, you can avoid the problem by putting every weapon in a different file. If there is only one weapon in the file, names will be unique and exporting should work as intended.
I updated the wiki
accordingly for now; suggesting one weapon per file for export purposes.