1. In a recent game I was constructing a wonder when the region was conquered by a neighboring enemy. I retook the region on my next turn but was no longer able to construct the wonder in the shared projects menu on my cities. The wonder foundation was still on that tile (so I could not construct anything else there) and the wonder was no longer availible to be built or placed. The wonder was still claimed by my civilization. I was also unable to claim any additional wonders. At least one other person on reddit had the same issue.