I found similar issue. But this only happens when I call “setZOrder” and “reorderChild” function.
Say there are 40 nodes on our layer, 20 nodes (T) on top of 20 other nodes (B). Sometime the B nodes appears on top of T nodes after I call “setZOrder” and then “reorderChild” function.
To “fix” the case, I add extra dummy nodes to group the nodes
See if it helps.