The settlers I have at the castle have all turned hostile. As soon as I turn up there, everyone starts shooting at me! Named characters, companions and turrets leave me alone but everyone else...

Has anyone encountered this?

Only thing I've encountered that is similar is randomly coming across hostile brotherhood npcs

Something similar happened to me last night at the castle. I was doing a mission when I saw it was under attack so I fast traveled and found a horde of raiders had invaded. I helped take them out but saw a few Settlers that had hostile red names too. After the raiders were all gone they turned their focus to me, so I panicked and reloaded a previous save before the raiders attacked.

I traveled to the castle and nobody was hostile, then I prepared my settlers for an attack. Right after the raiders arrived this time, any settler I accidentally injured during the fight became immediately hostile, and if anyone was hostile during the fight then they all became hostile after the raiders were gone.

Finally, I reloaded the save prior to the attack or the hostile raiders and I loaded a mini nuke, destroyed their whole squad and immediately turned around to see if my settlers hated me for it. Suddenly they were indifferent and continued harvesting crops. Stupid settlers.

I know this wasn't very helpful in regards to directly solvingbut hopefully understanding a bit more about the bug can help you figure out a resolve too. You may end up having to reload a few previous autosaves and visit the settlement on each one to see if the settlers are hostile. When you find a save where they're friendly, I'd wait around for a bit and make sure the settlement doesn't fall under attack. If it does, see if that's the event that triggered the hostility. If it is, kill the invaders before they ever get to your settlers. Best advice I got.

Do any of your weapons include splash or area damage? While defending a named trader from raiders,I must have clipped her with some area damage with my explosive pistol, because she aggroed real quick.

Hey. I'd turn hostile too if the guy that's supposed to be protecting me shot me! I don't care if he was trying to help me. He should have been more careful.

I don't think i would call that a bug, NPC's turn hostile when shot, accident or not. You can also lower your weapon for a chance to be forgiven. A better option to resolve hostile settlers would be nice, but there's always learning to aim better.

Or you can just kill 'em. It's not like there aren't ALWAYS more settlers out there.

what dont take that from your slaves, kill them and drag their bodies to the entrance as a reminder to all who would challenge you rule!

Me I'd just kill 'em and leave 'em for the molerats, but, hey, whatever works for you.

I had this happen today as well. Flew via vertibird to help defend The Castle and arrived to find a huge battle underway with Raiders fighting my Minutemen/Settlers while The Brotherhood of Steel were hovering above in another Vertibird and blazing away with the minigun at the Raiders. In the heat of battle I may have inadvertently shot at one of my settlers, because after the Raiders were dead they all turned on me. I legged it and then fast travelled back later, only to be attacked again.

Sadly I had to massacre my own Settlers and out of 16, only 6 survived because they were Minutemen who hadn`t gone aggressive. RIP peeps.

I had this happen with a single settler and was wondering if it was deliberate, but it sounds like bad AI now.

Sanctuary Hills got attacked by synths, I cleaned them out then got attacked by a single settler. I didn't know what to do, but Dogmeat took her down, and he wasn't even my companion. She turned out to be a synth, which is why I thought it was intentional.

If you attack friendlie's during combat THEY BECOME HOSTILE.

It was the same in Skyrim, companions are more forgiving but work the same way.

So either be more careful in combat and/or wait for a patch/mod that allows friendly fire.