I'm actually posting this for my bro. He was inside sanctuary, all was peaceful, then all of a sudden the settlers just started attacking each other. Piper started shooting his character as well!

The thing is, all stats were healthy, enough food and water, 80% happiness.

Weird, anyone experienced this as well?

One of the settlers may have been a synth? And the others found out?

Ah I see, so the Synth's will infiltrate later.