I upgraded to the latest LTS release and now some world-space canvas objects and children spawned from prefabs do not get placed correctly when I instantiate them and set their transforms
Has anything changed in that department, pehaps to fix some other bug?
First bug is in 2017.3.0 (and before) you could spawn a prefab with a canvas on, set the transform position, then set the RectTransform.sizeDelta without the position being affected.
Now setting the sizeDelta can effect the world position - a change caused by a bug fix surely (probably a 2017.3 patch release that went into 2017.4.0) You have to set the sizeDelta first.
Can you file a bug report, please?
It is not easy to create good reproductions of the bugs with this one, but try case # 1028051