This would be difficult to answer without seeing the blueprints that may be causing the problem. Did you use something like [Hide Actor in World], or did you use [Destroy Actor]? It appears to me that the default of the item is to ignore physics. If this was not the intended function, then at the very least it doesn’t seem to be re-enabling once it is spawned.
This may seem like a common question but it happens a lot: How are you controlling the boxes? As in, are they controlling themselves within their own blueprint? Or, are you using the world/player controller? A lot can go wrong when trying to use the object’s blueprint to control itself because events often end up getting called with a reference to the original instance.
Also, are those boxes starting out spawned (placed in the world via the editor), or are they being initially spawned using blueprints?