No, you misunderstand. I'm not talking about supply depots. I'm saying that object in the field might use some object or texture or whatever that is also on a supply depot or some other shielded object. An error in programming is applying a shield to an object that should not be shielded., such as a wall. Next time it happens look at what happens. I'll bet you'll see a shield impact and it looks exactly like a flat wall and not like it does when you shoot a player. There have been times where I didn't see anything and yet still I couldn't hit them but that doesn't mean a shield isn't there, maybe it doesn't have the files included to show shield impacts. Maybe that object has a shield but was made before the shield impact graphics were implemented in the game. I know enough about coding and basic game design to make the guess that this is what is happening but I don't have to expertise to explain it better or to confirm it. But I do know the number one rule of game design is recycle and re-use.

3D modeling is a pretty time consuming process and objects are frequently made from several different parts so you can easily isolate a certain part of it to make small changes. It's standard practice to reuse some of these parts you've created for something else by maybe scaling it, combining parts from different objects to create something new and so on. It's much easier to use what you already have than to make everything from scratch. So I'm guessing some component from a shielded object was used to create certain walls for example and part of the shield was inadvertently added to an object that is not supposed to have it. Just a wild guess though, like I said I'm not an expert.

EDIT-Just thought to also ask you, have you ever had this happen when they were completely in the open? Or is it only when they're next to some object? It only happens for me when they're next to something and never when they're just standing there in an open area. I apologize my first post wasn't very clear, my bad.