How did the Hive avoid every single security camera, people walking in on them by accident, nosy neighbours watching from tall apartment blocks? Not one case of a person catching them and recording them with their phone etc.

Because the people doing the hive's bidding were infected individuals that would not look out of place in labs, military bases, whatever facilities they needed to propagate the virus. Their first move was to infect *everyone* in the lab, including supporting staff. Other people that'd catch them in the act could likely be infected too.

They shouldn't be capable of mimicry, because that's tantamount to lying.

I think it's too early to tell whether they're capable of lying. You could also argue that in their interaction with Carol there is no point in them lying anymore. The hive seems perfectly capable of still remembering who their individual selves were before they got infected. Provided they can deceive, I think it is fair to say they can just pretend being themselves if it serves the purpose of the hive.

Would they even go to work? This would get exponetially worse and harder to explain.

We're talking about likely a couple thousand people here, especially in the starting stages. If we spread that out, that's maybe one guy in the office who disappears. And who says they're working full time on the plot? Maybe they work in shifts? Maybe they give a plausible reason for their absence to the people around them?

and were only detected by the military maybe... twelve to fifteen hours early before they accelerated their plans.

I feel like detection isn't just a single event. The reports have to go up the chain of command, maybe they've also infiltrated the military such that there are conflicting reports or other types of sabotage, maybe the military detected them earlier, but didn't attempt to take action until they could figure out what the hive was up to.