Unlike the standard Motion effect anchor which you simply move to where you want it, moving the Transform effect anchor is FAR less straightforward. Moving it also moves the whole clip around the screen.
You then have to change the Position coordinates to try to recentre the clip ....which then also affects the position of the anchor!
So you change the anchor, then the position, then the anchor then the position etc etc.. and then if you're lucky you end up with the anchor more or less where you wanted and the clip back where it was.
Surely I'm doing this wrong!? I don't understand it's behaviour. Can anyone enlighten me?
In most any effect with an Anchor position in Premiere ... you really need to set the Anchor position before doing anything else. Any change to the anchor position after you apply any other position change means you end up essentially chasing your tail.
That's one problem with working with anchors. I only use them when absolutely no other control will work.