Is there any way to find out why the happiness is dropping? I've actually been adding things that should increase happiness.

Sometimes I miss an attack that that seems to drop it. Seems I only get the 'pop up' now when the fight is over. Since patch 1.4 I've yet to get a pop up telling me a settlement is under attack.

I think having a Synth mole in the settlement sometimes affects it, but no real way to tell who they are until they attack.