This is one of the strangest bugs I've ever seen…
If I do a Relevanssi search for "a phrase in quotes" it works fine.
If I do a Relevanssi search for "blue" (one word in quotes) it works fine.
But if I do a Relevanssi search for "George" (the word George in quotes) or "any phrase with the word George in it" in quotes, I get a 403 forbidden error!
If I search for George without the quotes, it works fine.
But it also happens if I search for the phrase "any phrase with the word in it".
I must have something configured wrong. Is there an anti-George setting? :D