Hello everyone,
I am not aware of this issue being discussed before but then I'm new here.
So I was playing with buffs and ore discoveries and at some point I was unable to queue 3 buildings. I suspect it has something to do with demolishing unfinished copper mines or something similar. I can post a screenshot of 2-building queue and a "your building queue is full" notification if needed.
As I do not see any reasonable explanation, I consider this to be a bug. Perhaps there is a workaround, a reset of building queue of some kind perhaps?