Intended. There is a physical limit in the physical models we create for each aircraft type.
If you look in the aircraft folder there are 11 copies of each aircraft type (with a slightly different name). Each can have a unique skin in the sim. So if you are in a squadron so your player aircraft and your flight are maybe using already 5, or 6 or 7,8,9 of those whatever there's not a lot remaining to make unique elsewhere in the theatre of that type for example other squadrons that may be using the same aircraft type for example Albatros_DIII_early etc. Short of making dozens of more copies and making the sim even more massive.
Luckily we have zillions of other aircraft types in the air in campaign.
There's a "default" skin for each aircraft type and those get used in places where another skin cannot be found, or there is no more available free of that particular aircraft model in that mission.
In the next WOFF 2020 we have some extra features to increase the number of those other squads using the same aircraft type as the player flight.
