Deep Cover
I'm becoming convinced that your "composition" while using the Fiendtrapper might come into play. When you have a successful Fiend Plate, he compliments your use of the "rule of thirds" which is a photography concept for those who are unfamiliar. I'm starting to think that you either need to be facing the front-ish part of the mob you're photographing, or that the fiend trapper essentially takes a screenshot of your screen while using it and judging the usability on whether you can see the mobs clearly or not. Campaignemon Snap? Also, you can only trade plates that are Yagudo, Orc, and Quadav for your respective country. Campaign NMs tend to be a lot more successful and you can only trade one plate in per mob, so travelling to various Fortifications that are under siege and getting a photo of the mob type in the campaign wave as well as their NM is the best way to clear this operation. Just to be safe, I'd move in front of the mob as well as composing the mob nicely in the screen before I use Fiendtrapper. Please report any photographic failures if you do this as well.
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