11 is the best KC in terms of speed vs. profit.
11 and higher increases the number of runes you get
there's another threshhold higher than 11 (14 or 16 I think), that increases the number of boltracks you would get; but those are pretty worthless.
Well, I suppose that did shed some light on the problem
the position (3570, 3300, 3) does not exist within the barrows regions; so that is likely some kind of bug with the mirror client returning an incorrect player position. If that is the case, there's really not much I can do
It seems to work fine for me
You may have to post this in the Client bugs section, as the banking API used is written and maintained by the client developers. But the bug report would have to be more detailed (with a screenshot of bank window position and position of the item).
If I ever experience the bug myself, I will try to debug it and speak with the devs.
Adding