considering most groups have done problematic things, id say most groups are problematic.
blackpink has a culture appropriation problem, twice had the chaeyoung scandal recently and also have done cultural appropriation. bts had the namjoon aave allegations, cultural appropriation, and that one photoshoot at the memorial... straykids had racism allegations... anyway you get the point.
as far as who's the most problematic... id say bigbang for sure. if I remember correctly most members in that group have been in scandals, and those scandals are some of the worst i've ever heard of.