Correct me if I am wrong here but this was/is my thinking regarding the change.
1) When looking at the hard numbers or the forecast chart (such as below) you see a big drop coming...not only big but rather quickly
But when I see "change" I look at it two ways...
1) What is causing the change?
2) Is the structure of the "big picture" changing?
In assessing these two questions, what I gather is
1) There is some transient ridging which evolves and traverses the southern portion of the AO domain which leads to the big drop in AO which is further enhanced by the rather positive anomalies associated with the heights.
2) The big picture is not changing which is why it is still not a good pattern. The structure of the AO and Arctic domain remains...the TPV still remains quite strong, however, the most negative height anomalies just push a bit towards the opposite side of the pole (hence the "drop in AO").
Look what happens after this drop...the AO spikes right back up as that transient ridging either weakens or pushes east of the AO domain. I would even bet that when this drop peaks it ends up being slightly higher than forecast.