It's not bugged, once you have the quest to gather the May Mists, talk to Humaoid A and select the lower option (i.e. not the quest but the dialogue option on the bottom.) He will then send you to Where Snow Rose Grows.
It isn't specifically Sengoku recipes that cause the lag, but the large abundance of recipes in Smithing as a whole. Unfortunately, a lot of the recipes are inaccessible (such as PVP gear, Level 125 Von Leon gear, Level 130 Imperial gear, and Empress gear recipes, excluding the capes). I would say that the Smithing profession needs a cleanup.