Hi,
In this game [0.5.9.132]-ironheart-sinister_six-expert-(119)-(345800767).json, I was trying to thwart a side scheme with my allies, but I was only allowed to select the main scheme, as can be seen in this screenshot:
I may be mistaken, but I do not think there was anything in play preventing my from thwarting that side scheme with my allies. And, in fact, I was allowed to thwart with my hero, events and supports.
Thanks in advance!