Boolean values do not need to have parenthesis, im surprised that 'bool (true)' works at all, in fact! Technically, just using (bool) is legal but the parenthesis serves no purpose.
Just like you don't need to include the type name 'string&' when providing a string value, you don't need the type name 'bool' when providing a boolean value
SetEnemyDisabled("servant_grunt_1", true);
That is perfectly valid, and will work provided there are no other issues. I suggest that what happened to you is that you changed several different things, one of those changes corrected the issue you were having, but it was not the parenthesis around (true)