@monnikje That is true they should just work. This is very odd and unfortunately other than unsubscribing and subscribing again I don't know what else to suggest. Obviously I have never experienced a problem with them, nor have I had anyone else mention an issue. Sorry I can't be of any more help.

Props are not mods: when you subscribe to them, they should work. You don't activate them ingame.
I have unsubscribed and subscribed to not only the props and the building, but to all my mods/assets, and resubscribed to them. The problem is that when I look in the loading screen mod, even after subscribing to the Scout Gate and the Scout Flag they apparently are not loaded. They give the following errors:

Asset bug: Workshop asset uses private asset (ScoutFlagProp.Scout Flag_Data)
Asset bug: Workshop asset uses private asset (ScoutGateProp.Scout Gate_Data)

@monnikje That is very odd, it should work if you have subscribed to both. Make sure they are all activated within the game, or try deactivating or unsubscribe and subscribe again.

Even when I subscribe to the Scout Gate and Scout Flag, they still show up missing :(.