There is a bug in Mark's route where the fifth CG on page eight isn't loading, even though went through the scene and saw the CG multiple times.
It loaded for me and I unlocked it yesterday. Minor Spoilers:
I'm pretty sure it's locked to jerking off in Mark's room, opting for a toy, then using the one that reminds Grey of Virgil (rightmost one with a club symbol on the balls). Then when Simone asks you to choose, choose Mark and proceed as normal.