Thanks for the chapter!
Kangyi seems to be trying to get too chummy with MC. I bet she's up to something with Feng and had negotiated with him while he was up North, possibly in alliance with 3rd prince. Fengdai really doesn't know how to check things out. After hearing MC mention how a concubine who had done same dance had drowned she should've talked with her father about when and where to do dance along with making sure it wouldn't anger somebody, like the emperor, for some reason. Seems odd she'd do it there and then while Emperor is conducting court along with the doors being wide open in the middle of winter.
@rengetsu08 I think you're a little off. As far as having an affair I think their relationship was still platonic, but was way beyond what is acceptable. Also, it wasn't just the dance (in particular doing so barefoot and lightly dressed,) but the special earrings the concubine was wearing enticed the Fifth prince which was why 3rd prince told Chenyu to give the earrings from her crystal set to Fengdai in an earlier chapter. In any case, Fengdai dancing like that did accomplish her goal of getting the Fifth prince's attention, but reminded the Emperor of a past insult and could be interpreted as a slap on the face. Surprised Feng immediately went to his knees begging for forgiveness rather than running over and stopping Fengdai before bringing her over to apologize. Even if he apologizes immediately the situation is just going to get more and more worse as she'll just keep dancing until stopped as had been training to do it for at least an hour which will just make Emperor more and more angry as time passes.