why aren't nodes invalidated

Admittedly, I have a rather complicated shiny app and it is difficult to come up with a minimal example.

But, I came up with the following screenshot that shows a node (traj_targetPath) that is invalidated, but the following nodes traj_getPseudotime and following are still Ready. I am at the end of the reactlog and nothing is happening.

Under which circumstances is this possible?
traj_targetPath is a reactive and is dependent on input$elpiStartNode (as shown in the picture)

What seems to make a difference is to remove all "isolate()" statements, though this doesn't make much sense to me...