There is a bug in the Sancho gallery screen where if you click to the right of yuki's name(Roughly the position of Start in main menu) it starts the game, this bug is not present in the og gallery.
btw also for Quit button.
Actually it is an issue in the OG gallery (and other pages as well). This has been a VN issue forever which I used to fix and brought up to the dev many times on deaf ears. Because he keeps changing the menu system code I stopped "fixing" the issue tbh.
Here's what's going on (in layman's terms to be best of my ability at 4am on first coffee): This VN (as well as some others) use images as clickable buttons in an image map of the Main Menu. Circled in red are these zones:
Now, keep in mind where exactly these image mapping zones are, and in every single tab of the og Replay screen (Bios, Memories, etc) you'll find that ALL of the Main Menu's image button zones remain active on every single one of them. Because the menu code is so fucked up this impairs the SanchoMod and SanchoGallery screens as well (since they are integral to the VN's menu code).
So, in any of those screens if you click in any of the Main Menu's image button mapping zones (including the patreon zone, etc) they are active under the currently viewed screen and it's associated image button mapping (each sub screen has two image button mapping sets instead of one).
To summarize:
The dev attempted to resolve this via RenPy's modal feature but it's not implemented correctly, therefore RenPy keeps the MainMenu technically active while populating the new screens on top of the Main Menu screen instead of replacing the Main Menu screen.
That's the easiest way I can think of to explain it in the most non-tech language way. Hopefully that makes some sense (it's way too early in the morning here).
Regards.