My guess is that you've created a savegame in the closeup view of the cups trick. Is that right?
In that case you've encountered a known bug of Gray Matter. Gray Matter has a problem connected to the exit hotspots of closeup views.
One result is that if you save at a closeup view afterwards the exit hotspots are gone or don't work anymore. So you're stuck in the closeup view then. There was a patch released (probably already included in the gog release) so that the save option is grayed out if you enter the ingame menu using the ESC key. Sadly the save option is still active if you enter the ingame menu using the icon of the inventory bar. So it can still happen.
Another result is that the follow up location is connected to the exit hotspot. Normally it's the location from which you entered the closeup together with the current parameters. If you get the last points of a chapter in a closeup it's the start location of the following chapter together with the start parameters of that chapter. It sounds ok. If you got the last points of a chapter in a closeup view, leave the closeup view and you are transported to the next chapter. But there's a problem. If you got the last points and are still in the closeup view and now use the map the game loads the location you've chosen at the map together with the current progress. And now you're stuck in the chapter.
So my guess is you saved in the cups trick "closeup" view. Since this "closeup" view is the normal view with just the cups added you don't notice that you're still in a "closeup" view when the cups are gone (it's just technically a closeup view). This "closeup" view never had hotspot unrelated to the cups trick game and since there isn't even an exit hotspot now you get exactly a situation you've described. That's the reason for my guess.
You can solve the cups trick with the info from the magic book. So no need to save during this trick.
So with Gray Matter you should follow two rules connected to closeup views:
- never create a savegame while you're in a closeup view
- never use the map while you're in a closeup view
So to continue with the game you should load an older savegame, don't create a savegame from the cups trick closeup view (or any other closeup view) and then replay the cups trick. You should then be able to look at the fuse box and use the security door switch.
If you don't have an older chapter 6 savegame I can provide one.