some of tiles that 2x2 units occupy are near impossible to cast spells on

here i am trying to rip out my own hair in frustration.
as i try to cast a poison cloud on a particular tile occupied by a 2x2 unit and the game just won't let me.

 

i think whats going on is that maybe one or more of the 2x2 units tiles end up being bugged out somehow.
turning untargetable or something?
and it also seems to happen more often when your nearby spell presence only covers half the 2x2 units frame.