Hello arvedui78,
I am happy to see that you keep playing the game!

Regarding your questions:
ad1) This does not sound right. Size 8 is really a huge city and the number of citizens "removed" should be around 10. Do you have the save file right before you executed that state decision? I would have a look for sure.
ad2) Stables are in general able to specialize in more map item types (similarly to cities). I can only guess that some of the stables (with multiple specializations) were taken from an enemy who had access to more advanced technologies. Some specializations (this is defined in scenario) will be "kept" for you in the stable even you dont have that technologies (and some are reverted).
In your case, it seems like you have currently access to only one map item type (allowed to be built in stable) and the others were "acquired" with particular stables. Is it possibly that case? If not, I am also happy to have a look.

Thanks for the reply, Pavel!

Unfortunately I don't have the save files anymore... In the first case, the downsizing to population was around 1k!

About the second question, just to clarify: in principle, stables can keep adding different specializations?

Originally posted by arvedui78:

Unfortunately I don't have the save files anymore... In the first case, the downsizing to population was around 1k!

That's definitely not right at all. Wasn't there anything else like plague or earthquake as well?

Originally posted by arvedui78:

About the second question, just to clarify: in principle, stables can keep adding different specializations?

Ahh sorry, I was wrong, I just checked the mod file and it is set up for one specialization only. It that case it might be a bug. I will have a look if I notice anything.

One thing I forgot to mention, kind of important: I was playing a mod, the Ancient Mediterranean from zero, with the original map but where each player begins with only one city.

Originally posted by arvedui78:

One thing I forgot to mention, kind of important: I was playing a mod, the Ancient Mediterranean from zero, with the original map but where each player begins with only one city.

I see. In that case I cannot really guarantee that everything was correctly set up. Almost anything can be modified in inherited mods. As far as I remember that mod somehow modifies the way citizens are handled.

Anyway, the proper way to use the forced labor state decision seems to elude me a bit: everything that was under production in more than 1 turn gets cut down to 1 turn? Is that it? And the cost in resources and population depends on how many items were sped up this way?

The idea behind it is simple - you force people to work more than they are used to. This speeds up the construction process but increases costs and unhappiness.
The number of things which are speeded up this way is a bit random. Can be anything between 4-8 independent built/trained items.

The bug happened again, with the forced labor state decision; hundreds of pop points died, all cities leveled to 1. I tried locating the previous save file and repeating the bug, but to no avail. I couldn't even capture a screeshot, there was a problem with my steam interface or something...
What I can say is that I was using the Ancient Orient Mod.
And when this bug happens, it is never the first time that I am using this state decision.

Hello arvedui78,
try to hold CTRL when clicking on the game to load. This ensures the same random seed as there was when saving the file.