Dear Michael, I had the same issue and I solved the problem by manually installing libglvnd0 instead of libglvnd0-nvidia (which was automatically installed during the upgrade).
Please note that libglvnd0-nvidia provides libglvnd0 and comes from the non-free archive: I don't know why the non-free package was selected instead of the main one. Having done that, you can upgrade the system and X should work! See also https://bugs.debian.org/876220 Regards, Lorenzo Pinelli
