I had a look at your custom pushback and, the error was caused because the additional node you created in the middle of the taxiway was orphaned.
You could verify this by running the "Tools->Fault" finder in ADE: it will tell you there's an Open Link and an Orphaned Node there.
To fix this, remove your node, then add a new one, but be absolutely sure the taxiway blue line is highlighted when you click on it. If it's not, it will place a node very close, but it won't split the taxiway in two, as it should when you really "insert" a node. To be sure you did it correctly, run the ADE Fault Finder again.
But there's another issue, you didn't had to create a new node to begin with! This sentence at Page 33 of the GSX manual is the key:
The airplane will now be pushed towards one of these two nodes. It will not end up exactly over them, though, but it will be pushed the minimum amount needed to be aligned with the destination taxiway. Think as the two nodes as magnets...
The word "minimum" it's important. It means if you specify a node, the pushback won't try to go *there* but, it will use that information to know which direction you want to go, without any unnecessary travel. As soon the airplane is aligned with the destination taxiway, it will stop there, even if the custom pushback node is far away.
Have a look in the attached screenshot which pushback nodes I chose for your custom pushback, with an indication of were the airplane will end up in both cases. As you can see, it just did the right thing, regardless of the actual position of the nodes.
The coordinates are:
Y1 = 55.62614299 12.64162481
Z6 = 55.62662613 12.63822198