Shattered Kingdoms

And can you verify that there was no spell active that might have impeded your own guardian's vision?

The last time i visited the MC guardian a few months ago it sure as hell was aggro against me.

The only possiblity i can think of if the guardian's sight was unaffected is that their front row was completely sanced. If the battle was quick enough, they could walk in, have a 2nd or 3rd row char start the fight iwth you, get the stuff, and walk out. The whole time the guardian is deflecting off the sanc trying to start combat, which it does not spam nearly as effectively as players. Unlikely, but possible.

I recently walked with a none affiliated character into my guardian and it didn't attack. I also recall a harly once following me inside my keep and I let him follow me inside with the inner guardian, both times the guardian alerted me someone entered the inside but did not attack.

If you are grouped, i dont think they do.

Did the harlie have sanc?

Midnight guardian should be fixed now.