David,
Thank you for the sample images. I find no direct evidence of cause of the unwanted characters (n'n) in the file. What I did notice is that there are two linefeed characters at the end of the the Caption field, perhaps that threw off Getty's system when it processed the file?
Also, I don't see you using any of the Getty-specific fields that Photo Mechanic offers. Doesn't PM support the Getty fields you need, directly?
If you're able to resend/reprocess the photos, it would be interesting to remove the two linefeeds (just backspace over them) and try them again.
HTH,
-Kirk