Super late, though in case anyone still cares that the face is not being shown at max cum:
For some reason the 5th tier face is not being called(L02_Cha_Face05.rpgmvp).
I don't know where the missing call is and I'm far too lazy to search for it, but as an 'easy fix' a modified max cum pic works. (L12_Cha_FaceC03.rpgmvp)
Since at max cum this cum pic will be drawn in an higher layer above the face.
I have simply put both the face and the cum in one pic with the 3rd cum pic name, since this one is still being called.
Not the best of fixes, but a least no missing face anymore.
Simply unzip and overwrite the file in www/img/pictures.