photos library shows blanks after updating the library
I hate to answer the obvious, but now that you are updated on the OS, I would try once to repair again and open a case with Apple. Worst thing is you spend a little time and someone here has a better answer in the mean time.

https://support.apple.com/en-us/HT204967

In the past there was a repair and a rebuild, but it seems Apple has streamlined their advice before you seek their help. I would hate for you to take more drastic action if there is a bug they have to fix on the rendering and processing side. What if your library is (and was) intact and the code needs fixing?