I am using a custom race that is synthetic and a slaver, so I'm using both synthetic and Dregnin tech. Forced Labor Camps no longer increase the population cap and I don't see the ability to build a city. Can you make a fix for custom synthetic races that are also slavers?
I have never tried this combo out, but I just gave it a shot now, and it's interesting. Every planet I settle gets 8 max population, absolutely unchangeable with any (early?) buildings. Building more population is disabled after 8, but you can go over the max by dropping colony ships on a full planet. This gets tedious, but since Synthetics don't have to worry about morale, you can just keep doing it to overpopulate. You don't lose any population from "negative growth" like with inferior organic races.
The Slaver research and production improvements totally outclass Synthetic buildings - but at least they benefit from the weird social production adjacency bonus of the Yor resource extractor.
The Slave Master citizen is very powerful for this combo, especially after you have set up an over-max-population production world.