Huh, I've not had that reported yet for E7 (or at all). Let me look into this.
Okay, since that is a main story scene and I've not had that ever been reported before, I am inclined to think it might be an issue with a driver or incompatibility on your PC. You are not alone in this though, a check of the Renpy forums do show a few others do have this from time to time but it is pretty rare. Usually it's reported as a problem with video drivers, so make sure those are up to date. Another solution you can try is to press SHIFT+G and selecting a different rendering mode.
If neither of those resolves it, please let me know, I will dig into it further.
DMD47