I’m not as into nutrient knowledge as some of the others, some of who make their own blends, so hopefully one of them will comment, but I suspect the answer will be that it is too much nitrogen for bloom. Once bloom starts you need something with reduced nitrogen. Apparently to much N can reduce your bud growth/size.
I wouldn’t think you need to flush when changing to another nutrient, as long as there isn’t a nutrient buildup happening already. Just give them plain water on your regular cycle.