Proxy mines used to get stuck in a repeating 'throwing arc' animation and would never deploy, if they were thrown on an existing mine at a certain angle.
Guardian's Sky Shield drone will also do this. If thrown at certain in-game objects like dead merc ragdolls, or sometimes a disabled EV, it will repeat a similar animation and will never deploy.
Steps to reproduce:
Throw Guardian's Sky Shield at a dead (grayscale) merc
Throw Guardian's Sky Shield at the corner of a stationary EV
Unlike Proximity Mines and ammo packs, the drone isn't required to completely settle on the ground, or to avoid landing on top of another drone (another mine or ammo pack). If there's something in its path or it can't bounce off, it can still float upwards and deploy as a last resort.
Thrown deployables can disappear or spawn at a previous location when thrown at in-game objects like the EV or other players, but that's not what this bug is about.