I know there is a “Find the Loot Crate challenge” that can come up, but as I see it if your ops are high they go for one of those 1-3 You mention.
About that turret challenge… it only came with my OPs starting at 0-10. So I Guess that means the game has “Challenge Tiers” and once you got a lot OPs To start with easy “Spot the loot Crate” Challenges won’t Show up.
The turret Side Objective felt more like a Tutorial than a challenge… since if you try to win That Brute Spam as lets say… Rath, you Probably won’t be able to protect your Rally Beacon.
But “Activate the Anchors” sounds like Triggering some friendly Thralls, which would help to make it feel like a Rebellion rather Than Attikus Trashing Arias Place.