Thank you for bringing this to our attention, we are aware of this issue and working to resolve it as quickly as possible.
In the meantime, you can still close the dialogue by clicking the area where the 'X' should be on the top right of the window. The 'X' to close it is there, it's just invisible.
I've put this post in 'Voting' in case others are seeing the same thing and will advise when we have it fixed.
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