! red symbol what is it? also bools do randomly fail

obtained while using subtract bool between the main gray solid, and the fucsish solid ;

bools, do seem to randomly either work and not, sometimes a problematic bool, might work by itself, sometimes won’t, other times it will but weirdly, if I do select delete solid after subtracting, it will not and viceversa, or they do work, but they do let an opensurface with two faces missing from the orignal geometry, like this

It usually happens on bad intersections. Can you post your Rhino file?