I think that we should had expected the instability of this particular symmetric form of the Fig.9 “stopper”, given that the corresponding ( I claim I “see” a genuine correspondence here…) symmetric form of the Fig.8 "stopper’ ( the Pretzel-like one, shown at the attached picture, generated by a symmetric cut of the closed 4.1 knot ) is also not very stable. After all, as I had noticed at (1), there is a unexplained pairing between the Fig.8 and the Fig.9., then a gap, which should not be there ! 
( and so it should had been expected that it was not expected…) and then a pairing between the Fig.10 and the Fig 11.
A first explanation for this instability was attempted at (2) - where one can also see a picture of the retraced Fig.9 knot.
When this oblique / diagonal element passes straight through, and in between, the two interlinked overhand-knot-shaped parts of the knot, as in ABoK#582, and not around them, on the surface of the nub, as in ABoK#525, this problem disappears.
- http://igkt.net/sm/index.php?topic=3838.msg25911#msg25911
- http://igkt.net/sm/index.php?topic=3236.msg30470#msg30470
