Hey, thanks for the extra information, unfortunately as I thought, it didn't really help that much.
So from what I can see now, it really shouldn't be a GPU or CPU issue and that brings it down to a few other things like these:
1 - Power saving features, if these somehow trigger while the game is running then these FPS drops can happen.. but I've basically told the game to use as much CPU as possible to prevent this from happening so it should be unlikely this is the issue.
2 - Windows had an update a while ago which caused some GameMaker Studio games to run at reduced framerate, never had this issue myself so I don't really know how bad it was but there were a bunch of posts over on the GameMaker forums about it.
No idea if this has been fixed in another windows update either.
3 - 240Hz monitor, I've read about issues with this on the forums as well (not limited to 240Hz but high refresh rate monitors in general) but never really had any issues myself running 120Hz or 144Hz monitors.
So not sure about this one either.
So basically what I'm saying here is that I have no idea what the issue is really and as such there is nothing I can do to fix it right now.
And with all this being said, this issue may or may not be solved once I update the demo again since the game is in the process of being ported to GameMaker Studio 2 which is a much more up to date version of the engine.
This also means the game will be switching over from DirectX9 to DirectX11.
So yeah.. this issue is on the backburner for now since once I release the new demo any old issue like this might become irrelevant.
Anyway, thanks for trying to help me out and sorry this post became quite big, it's just hard to explain these things in short.