Just encountered this moments ago and came to the forums to see if anyone else had experienced it.
Same thing with the phantom +30 difficulty here on a pair of 418 Flame-Touched boots with Flavor Pocket. They had the minimum rank set to 5 (as they should when I’m guaranteeing it with an insight) but because the displayed difficulty was 400, I was unable to even hit the recraft button. They were sensibly nervous to go ahead and try anyway with a R4 min. while still using the insight to clear the 370 of what the difficulty should be, and I missed out on the craft.