I had facing this problem more the 4 times in the past 2 weeks. On a plane I have my own load out and I choose it before spawn in to battle. But after the plane spawned it auto change to default load out when this plane is stock. (For example I custom load 4 R60M+2 R27ER for my Mig-29 but when the plane spawned it changed to 2 R60M+2 R27R). I made a bug report ticket but it keep saying I don’t have enough material to support it.
Delete the loadout completely, Remake the loadout and then restart the game
Also clear the cache folder possibly in the same instance.