Some SPAAs that use radar-guided missiles appear to spawn with only one missile available. This issue occurs with the free SPAA provided by the game, although I am not sure if it also affects researched vehicles.
When using the free SPAA, the vehicle spawns with only one missile. If you try to replenish the missiles using an ammo crate, the missiles are not replenished. The ammo crate simply appears next to the vehicle without adding any additional missiles.
If anyone could take a look into this issue, here is a video showing the problem. My friend did not capture the exact moment when he spawned, but you can clearly see that he only has one missile and is unable to replenish it using the ammo crate.
Thank you for looking into this