@Marindor this just happened a few minutes ago in my main Beta city. I soon as I clicked the Evolve button, the screen went completely black. The mouse pointer still has the normal Elvenar icon, but just a totally black screen.
@Karvest this may be a totally different bug, if you want to start the bug thread for the credit.
from the developer tools display for the tab:
Uncaught Cannot cast {
_vo : {
next_state_transition_in : 9,
__clazz__ : UpgradingVO
}
} to {
__name__ : de.innogames.strategycity.main.model.vo.entityStates.api.IProductionEntityState,
__isInterface__ : true