Your intuition is correct here. Your lack of updating could be due to a the cache bust parameter. The cache bust parameter solves the issue of a browser caching data when in reality we want it to re-load. Some more basic inoformation can be found here:
But how do you do it in a tree view with Mendix? To do that, set up your tree view and when you select your entities, you have the option under the '2) Advanced' tab of the Entity configuration menu to set a 'cache bust parameter' for the entity you are setting up. The cache bust parameter should be something that changes when you want the tree view to update. In the microflow that sets your associations or moves things around, you could do something like random() to ensure that the cache bust parameter will change that the grid will be re-loaded.
In the widget itself, beneath the cache bust parameter attribute selection, you can get some more information about how it works in relation to children, but I hope this is enough to get you started.
Thanks! I now intend to switch a boolean at every change. What would be the syntax for that? I now have something that gives an (EOF at 'if') error, namely:
false if true