When I click on the "residents" link within an arcology, it instantly sets workers and residents to 0 and then slowly fills back up. I have done this with 4 different arcologies on my map with the same result.
Running v47 on downloaded client for OS 10
It is not just arcologies, really. Most colonists in a big colony are simulated/virtual, but when you click to look at the residents or workers of any given building, it has to destroy all of the virtual colonists and create new real/non-virtual colonists, and generate new stats for each one, which can be a large CPU/memory load on a giant building like the arcologies, one of the reasons I was hesitant to add them in to begin with.
The ability to see the list of residents in a building is really a relic of the way the engine used to work with every colonist being unique, and it will probably be removed eventually.
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