Short description:
You can't always see the percentage of an upgrading building, even when you adjust the zoomlevel. Trees or mountains are hiding it.
Screenshot:
The building on the left, partially hidden by trees
Possible cause:
Specific locations on the map where the view of the building is obstructed by trees or mountains.
Prevention:
Don't build there
Workaround:
No useful workarounds.
Related:
Original thread(s): 1