I've never had a problem with stability in my own cities but cities under my occupation generated rebels before when war lasted long enough. In such cases rebels were comprised of 3 units of my strongest melee unit researched at that time.

By the way, I think it's peculiar that an occupied city can produce my own most advanced melee unit despite the fact that occupied city is technically not mine yet and AI whom city still belongs to hasn't even researched tech to produce these units (or simply does not have the ability to produce them since they are my culture's unique unit, like when this happened with Promachoi in Ancient Era).

I've never seen rebels out of ranged units, though.

el-Fakir wrote:
By the way, I think it's peculiar that an occupied city can produce my own most advanced melee unit despite the fact that occupied city is technically not mine yet

There are still some serious issues about "ownership" of occupied cities.  The game treats cities that are occupied by another empire as belonging to the occupying empire in far too many ways.  As you've seen, it'll spawn the occupying empire's melee troops as rebels; it also treats the city as the occupier's for Civics and Science osmosis (benefitting the occupier with science and potentially forcing civics changes upon the occupier as well) and I've even unlocked new civics and events in the occupied city that were really meant for peacetime.

In an earlier patch, occupied cities' appearances also changed so that all the decorative buildings suddenly changed to the occupier's culture.  It was really jarring.  I think they've fixed that, at least.

The Soviets remain broken like this, they not only can enjoy CS boost that at some point becomes impassable even with superior tech, they'll also spawn a bunch of rebels that will twiddle their thumbs or start swarming the surrounding areas, because they can't hope to stand against the supercharged Soviet militia, not to even mention their regular armies.

That's why I think there should be either hard cap on amount of Arms Factories (my idea was having them placed only over existing Strategic Resources, preferably with additional restriction of one per resource type) or they should be a special type of district available to anyone in Contemporary (so that anyone could pump their CS up with weapons) with some special, unique quirk.

Cheddahbeast wrote:

I recently played a MP game where a friend of mine chose Soviets as their final era culture.

In this game they had built 15+ arms factories , yielding a whopping -150 stability on all their cities; I thought, ok, they will pay for this in revolution FIMSI and rebellions....however...despite them having armies of 70+ strength Soldaderas, the rebellion spawned armies this stability crisis were 3 unit armies of HORSEMEN. Which was not particularly punishing in relation to the 15+ strength is was supplying their units.

Is there a clear understanding of how rebellion armies are spawned - or rules that define the number, type, and cost of the spawned units?

Sounds like a bug, so I am going to move the thread to the Bug Report.
And then we are going to need your save files and diagnostic (and is a multiplayer, if possible the same with your friend).

• Saves: Please provide the last two auto-saves from when the issue occurred along with any other relevant saves.
  • PC: \Users\[username]\Documents\Humankind\Save Files
  • Mac: This is hidden in the Libraries folder. You will need to do an internet search to find specific steps for your OS. Once the libraries folder is revealed, they are in /library/ application support/humankind/Save Files 
• Diagnostic files: These files need to be compressed as a zip or rar file or the upload will fail! Located by default: 
  • PC:\Users\[username]\Documents\Humankind\Temporary Files 
  • Mac: Select the correct file by looking at the name like "Diagnostics - 2020'10'11 @1407'46''" that gives you the date and hour which should correspond to a save file