https://fiddle.sencha.com/#view/editor&fiddle/2g5m

1. When bufferedRenderer==false and there are empty expandable child nodes in expanded state, collapsing/expandin of parent node several times cause error and parent node cannot be expanded anymore.
2. disabling expand/collapse animation fixes this issue, but expanding parent node now adds extra offset to this node.
(Ext JS 6.5.3.57 - Gray)

PS In my real same case problem reproduces even without expandable empty non-leaf child node, but I could n't reproduce it in the isolated fiddle