There are four of these on the dome of Hagia Sophia. Most of them were visible when I was there in 2013. Maybe one was hidden by the scaffolding.
These are not new!
> Another of the four mosaics was uncovered in 2009. It had been hidden under plaster and metal for 160 years.
I remember Hagia Sophia from 1954. I was a tad but I remember it. There was some scaffolding and restoration work then, too.Istanbul was a much friendlier place for Americans then.