they spawn out of thin air, is there a bigger spaceship larger than the Firebird that they teleport from, is the spaceship invisible and directly above us
Until now we don’t know.
Some possibilities:
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A base station somewhere, which we didn’t find yet. It has a launch system which catapults the pods to their destination.
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A dropship, which drops them at the requested destination.
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The russian space station MIR with a machine construction- and drop pod launching module.
Each of them could explain, where the pods come from.
The first one is the most lorefriendly solution as it would explain, why fnix just seems to be operating in sweden. The great island in the upper east could be a good location of this base.
The second one doesn’t make much sense. Why does it just operate over sweden if it could also fly to every other country? Why is it still flying and wasn’t attacked by soviets, nato or other forces?
The third one is my favorite one, as it would fit in as missing piece for the reason why the soviets did this massive attack on sweden/fnix. And it would fit in the time. But again, why just focussing on sweden, if dropped machines could reach every country on earth?
Maybe it’s all wrong and it’s just as it is… A non explained game mechanic.
This is the most reasonable explanation. A Russian MIR would not drop both the Sweden machines and the Soviet machines just so they could fight each other.
But the soviet machines aren’t dropped in a pod like the swedish ones (at least hunters and runners) are…
The soviets came by landfall with hovercrafts or by air (firebird).
I don’t think FNIX has the capability for huge aerial transports just yet. Far more likely, they are meant to be launched from somewhere nearby. Where and how, that’s unknown.
Sadly you didn’t use the word “yet” in your last sentence.
Ok, FNIX hacked MIR (sorry, I can’t let that fall down) or has a base with launching capabilities for those pods somewhere we don’t know or don’t get to see (yet).
I think there must be additionally a larger tunnel network than we know. Between himfjäll and Östertörn and this third large island.
Imagine a fast travel rail system down there 
I always assumed they were fired off like artillery from a warehouse type location that housed all the robots after production.
My option 1… I always thought they are launched from Norrmyra, but I dropped this idea after landfall.